LOS 
ANGELES 
COUNTY 
MUSEUM 
CONTRIBUTIONS 
IN SCIENCE 
NUMBER 179 FEBRUARY 25, 1970 
GEOGRAPHIC VARIATION AND SYSTEMATIC 
STATUS OF MEXICAN LYRE SNAKES OF THE 
TRIMORPHODON TAU GROUP (COLUBRIDAE) 
By ROY W. MCDIARMID AND NORMAN J. SCOTT, JR. 
Los ANGELES COUNTY MUSEUM OF NATURAL HISTORY    ?     EXPOSITION PARK 
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Editor 
GEOGRAPHIC VARIATION AND SYSTEMATIC 
STATUS OF MEXICAN LYRE SNAKES OF THE 
TRIMORPHODON TAU GROUP (COLUBRIDAE) 
By ROY W. MCDIARMID1 AND NORMAN J. SCOTT, JR.2 
ABSTRACT: Geographic variation in lepidosis and color pat- 
tern was studied in the nominal species Trimorphodon collaris, 
jasciolata, forbesi, latifascia, tau, and upsilon. Specimens were 
grouped into seven geographically separated samples which were 
then compared. Ranges of most characteristics overlap broadly; 
others vary independently and discordantly. Ventral-subcaudal 
scales decrease from north to south. Snakes from the Balsas- 
Tepalcatepec Basin have fewer dorsal bands than do snakes from 
other areas. They also have a relatively uniform head pattern. 
Specimens from other areas have a complex head pattern con- 
sisting of prefrontal bars, interocular bars, and discrete parietal 
marks in various combinations. Head pattern and body band 
analyses indicate limited genetic exchange between the Balsas- 
Tepalcatepec Basin samples and those from other areas, appar- 
ently the result of secondary contact in southern Jalisco and 
adjacent Michoacan. The Transverse Volcanic Range and the 
Sierra Madre del Sur apparently are effective in restricting genetic 
exchange. 
The above nominal species are assigned to the synonymy of 
Trimorphodon tau. Trimorphodon tau tau is maintained for the 
foothills and plateau populations and T. tau latifascia (new com- 
bination) is assigned to the Balsas-Tepalcatepec Basin popula- 
tions. Trimorphodon tau is redescribed and its distribution 
delimited. Character variation in a brood from Puebla approaches 
the variation typical of the entire Puebla sample. 
INTRODUCTION 
In the years following 1935, rather extensive collections of amphibians 
and reptiles were made in Mexico. Early reports on many of these collections, 
culminating in the Mexican checklists by Hobart M. Smith and Edward H. 
Taylor (1945, 1948, 1950), are extremely useful in elucidating the distribution 
and relationships of the many components of this complex herpetofauna. Dur- 
ing the past 15 years, reports on collections from various parts of Mexico have 
continued to appear. Unfortunately, some of these reports have confused rather 
than clarified our knowledge of the distributions and systematics of certain of 
the Mexican species (see Duellman, 1966, for additional discussion). An 
example of such confusion is found within the snake genus Trimorphodon. 
1Research Associate in Herpetology, Los Angeles County Museum of Natural His- 
tory and Collegiate Division of Biology, University of Chicago. (Current address: 
Dept. of Zoology, University of South Florida, Tampa.) 
2Biological Sciences Group, University of Connecticut. 
1 
CONTRIBUTIONS IN SCIENCE NO. 179 
All 12 nominal species of Trimorphodon have been reported from Mexico 
(Smith and Taylor, 1945). Smith (1941) divided the genus into two apparently 
natural groups. The biscutatus group, characterized by large chevron-shaped 
marks on the neck and head, included five nominal species {biscutatus, lambda, 
lyrophanes, paucimaculatus and vandenburghi) that range generally from the 
southwestern United States southward through the Pacific lowlands to Costa 
Rica. The tau group, characterized by a light, transverse nuchal collar of vary- 
ing width, included seven nominal species (collaris, fasciolata, latifascia, tau, 
upsilon and vilkinsonii) whose ranges encompass upland and mountainous 
portions of southeastern New Mexico, southwestern Texas and Mexico, north 
of the Isthmus of Tehuantepec. 
We became interested in the Trimorphodon tau species group in the course 
of an extensive study of the herpetofauna of Sinaloa, Mexico (Hardy and 
McDiarmid, 1969). In attempting to allocate specimens, we realized the need 
for a revision of this group of snakes and so began a study of the geographic 
variation and systematic relationships among the described forms, with empha- 
sis on the zoogeographic implications of the distribution of specific character- 
istics. 
HISTORICAL REVIEW 
Cope (1869) described Trimorphodon tau from a single specimen col- 
lected by Sumichrast, supposedly from the western part of the Isthmus of 
Tehuantepec, and Trimorphodon upsilon from a specimen collected in Guada- 
lajara, Mexico by Major (see Zweifel, 1959 for discussion of this collection). 
Later in the same year, Peters (1869) described Dipsas biscutata var. 
latifascia from specimens collected in Puebla by Berkenbusch. 
These descriptions were the first for representatives of the tau species 
group, though specimens of these species were known previously. Jan (1863) 
listed four specimens of Eteirodipsas biscutata, one from Mexcio. Nine years 
later this same specimen was illustrated in Jan and Sordelli (1872) and listed 
as part of the collection of "Westphal-Castelnau a Montepellier." The Mexican 
specimen definitely is not Trimorphodon biscutatus (Dumeril, Bibron and 
Dumeril, 1854), nor is it representative of a species of the biscutatus group as 
presently understood. In fact the color pattern, especially of the head (Jan and 
Sordelli, 1872: vol. 3, livr. 39, pi. 1, no. 3), is similar to the pattern of the holo- 
type of Cope's Trimorphodon upsilon. 
Cope (1875) described a fourth species of the tau group, Trimorphodon 
collaris. This specimen, also collected by Sumichrast, was from Orizaba, Vera- 
cruz. In 1882 Sumichrast pointed out that the type specimen of Trimorphodon 
tau was collected near Quiotepec, between Techuacan and Oaxaca and was 
not from the western part of the Isthmus of Tehuantepec as stated by Cope 
(1869) in the original description. In this same publication, Sumichrast (1882) 
listed "los individuos tipicos" of Trimorphodon collaris from Tuxpango, near 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 3 
Orizaba, Veracruz. However, in the description of T. collaris Cope (1875) 
made no reference to specimens other than the type. The location of any addi- 
tional specimens of T. collaris collected by Sumichrast is unknown. 
Gunther (1895) pointed out the similarities between Trimorphodon tau, 
collaris and upsilon, and referred his specimens to T. upsilon. Gunther con- 
sidered Peters' latifascia synonymous with Trimorphodon biscutatus. Boulen- 
ger (1896) recognized Trimorphodon tau and T. upsilon as distinct species. 
Boulenger followed Gunther's suggestion and included Trimorphodon collaris, 
as well as Trimorphodon biscutatus latifascia (Peters), in the synonymy of 
Trimorphodon upsilon. 
Taylor (1939) reviewed Mexican species of Trimorphodon and revived 
Peters' name latifascia for specimens from Puebla and Morelos. Taylor recog- 
nized T. upsilon and T. tau as distinct species but considered T. collaris synony- 
mous with T. latifascia. 
In 1941 Smith surveyed the genus Trimorphodon and established the two 
species groups. He considered Trimorphodon latifascia, T. upsilon, T. tau and 
T. collaris distinct species. In addition Smith (1941) described two more forms 
in the tau group: Trimorphodon fasciolata from Tzararacua Falls, Michoa- 
can (one specimen) and Trimorphodon forbesi from San Diego, Puebla (one 
specimen). 
After examining specimens of Trimorphodon from Michoacan, Schmidt 
and Shannon (1947) suggested that T. fasciolata might be conspecific with 
T. latifascia. Davis and Smith (1953) and Peters (1954) demonstrated that 
these two forms probably were representative of a single species. 
Smith and Darling (1952) examined some specimens from Tamaulipas 
and San Luis Potosi and regarded Trimorphodon upsilon as a subspecies of 
Trimorphodon tau. Martin (1958) confirmed the conspecificity of these forms. 
Duellman (1961) concluded that data were inadequate to support the 
retention of upsilon as a subspecies of Trimorphodon tau. He regarded Tri- 
morphodon tau as a monotypic species that has a highly variable color pattern. 
Thus, if the systematic changes since Smith's revision (1941) are accepted, 
there are currently four species in the tau group, Trimorphodon tau, collaris, 
forbesi and latifascia. 
Jones and Findley (1963) suggested that T. vilkinsoni might be related 
to T. lambda, a member of the biscutatus group. 
METHODS AND MATERIALS 
We have examined all known specimens, including holotypes, of the 
following nominal species of the Trimorphodon tau group: tau, upsilon, col- 
laris, latifascia, fasciolata and forbesi. Locality, sex (determined by dissection), 
and the following features were recorded for each of the 197 specmiens: num-. 
ber of ventral scales (counted according to the method outlined by Dowling, 
1951), number of subcaudal scales including the tail tip, total number of 
CONTRIBUTIONS IN SCIENCE No. 179 
ventral and subcaudal scales, nature of the anal plate (divided or entire), 
number of supralabials, supralabials that contact eye, number of infralabials, 
the infralabial that is first separated from the chin shields by small gular scales, 
number of loreal scales (all scales between the preocular and nasal scales), 
number of preocular and postocular scales, and the number of primary and 
secondary temporal scales. The dorsal scale rows were counted one head 
length behind the parietal scales, at midbody and one head length in front of 
the anus. The number of scales in the light collar counted on the midline was 
recorded, as was the number of body and tail bands or blotches. The first cross 
band that showed any indication of splitting (the presence of a light center on 
the midline) was recorded. For each band-interspace-band sequence the num- 
ber of scales on the midline was counted beginning with the first dark band- 
light interspace-second dark band, for the seventh dark band-light interspace- 
Figure 1. Distribution of Trimorphodon tau in Mexico. Each dot represents a locality 
or localities of one or more specimens. Solid dots indicate specimens examined; circles 
indicate additional specimens or literature records. Samples analyzed are lettered A 
through G. 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 5 
eighth dark band, and at equivalent intervals along the body of the snake. In 
all instances the band-interspace-band sequence immediately anterior to the 
vent was counted. Detailed drawings of the dorsal head pattern were made for 
each specimen. 
Specimen localities were plotted on a topographical map of Mexico and 
grouped into seven geographical units (Fig. 1). These seven samples, here- 
after referred to as populations A through G, include specimens from the 
following areas: 
Population A (25 specimens,?from localities in the foothills of the Sierra 
Madre Occidental of southern Sonora and northern Sinaloa. These localities 
are separated from population B to the south by nearly 480 kilometers. 
Population B (15 specimens)?from localities in the upper drainage of 
the Rio Santiago and its tributaries in Nayarit and Zacatecas and from the 
general vicinity of Guadalajara and Lago de Chapala in Jalisco and adjacent 
Michoacan. These snakes probably are continuously distributed in suitable 
habitats northward through Sinaloa, as indicated by two specimens from 
western Durango, but are separated into two populations, A and B, because 
of the lack of adequate material from the intervening area. 
Population C (14 specimens)?from localities in Tamaulipas, San Luis 
Protosi and Hidalgo in the eastern drainage systems of the Rio Panuco and 
Rio Tamesi. There are six specimens known from within the 400 kilometer 
hiatus that separates population C from population B, the latter of which is 
restricted to western drainages. 
Population D (20 specimens)?from localities in central Oaxaca. This 
sample is situated about 480 kilometers southeast of population C with only a 
few specimens known from the intervening area. The uplifted southern section 
of the Mexican Plateau effectively separates populations C and D. 
Population E (51 specimens)?a large sample from the vicinity of Chil- 
pancingo, Guerrero located in the central part of the Sierra Madre del Sur. 
These localities are isolated from sample D by the eastern extension of the 
Sierra Madre del Sur and the mountains in northwestern Oaxaca. 
Population F (25 specimens)?from areas in northeastern Guerrero and 
adjacent Mexico and Morelos and from southwestern Puebla. These localities 
are in areas drained by the northeastern tributaries and headwaters of the Rio 
Balsas. Population F is separated from E by the arid Balsas Basin and from D 
by the mountainous areas of northwestern Oaxaca. Population F is separated 
from sample C south of the volcanic peaks and high southern portions of the 
Mexican Plateau. 
Population G (19 specimens)?from parts of Colima, southern Jalisco 
and western Michoacan. These localities are situated in areas drained by the 
Rio Armeria and Rio Coahuayana (Autlan and Contla, Jalisco and Colima) or 
by the major northwestern tributary of the Rio Balsas, the Rio Tepalcatepec 
(Michoacan). This sample is isolated to the northwest of E by the arid Balsas 
6 CONTRIBUTIONS IN SCIENCE NO. 179 
Basin and to the south of B by the Transverse Volcanic Range and western 
portions of the Mexican Plateau. 
Specimens removed from the geographic range or topographically iso- 
lated from these units were considered separately. In other words, we did not 
extend the geographical coverage of our units to accommodate individual 
specimens. 
After the seven groups were established, the meristic, scale and pattern 
characteristics were compared within each unit and among the seven units. 
GEOGRAPHICAL VARIATION 
LEPIDOSIS 
Ventral and subcaudal scales.?Ventral scales vary from 20-231 in males 
and from 210-243 in females. Subcaudal scales range from 61-85 in males and 
from 55-80 in females. Females average 2-11 more ventrals than males in the 
various populations. However, males on the average possess 8-11 more sub- 
caudals than do females in the same population. The relatively shorter body and 
longer tail of males, as indicated by fewer ventrals and more subcaudals, appar- 
ently is the result of their more anteriorly placed cloacal opening. This condi- 
tion is probably an accommodation for the relatively long hemipenes in the 
tail. The converse probably is true of females which have a longer, more 
bulky body to accommodate eggs (Klauber, 1956:167). 
The number of ventral and subcaudal scales in snakes is indicative of the 
number of vertebral segments (Dowling, 1951:99). To test the assumption 
that there is little or no sexual dimorphism in the total number of vertebral 
elements in members of the same geographic population, we analyzed the 
number of ventral plus subcaudal scales for males and females in each of 
the seven samples using the Student's t-test. No significant differences (95 per- 
cent level) were found. Therefore, for purposes of analysis, we combined the 
ventral and subcaudal counts of males and females in each population. 
The ventral-subcaudal scales range from 265-319. The higher numbers 
are characteristic of the northwestern population in Sonora and Sinaloa and 
the lower numbers are from the southern population in Oaxaca. Variation in 
numbers of ventral-subcaudal scales in the seven populations is illustrated 
(Fig. 2). The relative geographic positions of specimens from localities outside 
of the geographic limits of the prescribed populations are plotted by number 
in Figure 2. 
There is a north to south reduction in the number of ventral-subcaudal 
scales within population A. The specimens from southern Sonora have 298- 
319, x = 307 (N=ll). Specimens from the Rio Fuerte in northern Sinaloa 
have 300-306, x = 303 (N=4). Specimens from north central Sinaloa have 
293-308, x = 303 (N=10). Two specimens from Ventanas, Durango (300 
and 302 scales), and a specimen from the vicinity of San Bias, Nayarit (294 
scales) are the only known specimens from the 480 kilometer distance between 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 
populations A and B (Fig. 2, Nos. 1-3). Their counts are intermediate and 
suggest that additional material from the intervening area would show that 
the north to south reduction in the number of ventral-subcaudal scales ex- 
hibited in population A continues into B. A specimen from La Cumbre, Jalisco 
(Fig. 2, No. 4) has 292 ventral-subcaudal scales. 
Within population B, three high counts (299, 299, 303) are characteristic 
of specimens from northwestern localities of population B, at Barranquitas, 
Nayarit, and near Magdalena and Bolanos, Jalisco, respectively. Two speci- 
mens from the southeastern parts of population B near Emiliano Zapata, 
Michoacan have low counts (282, 287). 
G - 
A  H   (25) 
B 
C 
D 
E 
F 
(15) 
(9) 
(20) 
(44) 
(24) 
(19) 
260 270 280 290 300 310 320 330 
Figure 2. Statistical analysis of the number of ventral plus subcaudal scales in popula- 
tions A through G of Trimorphodon tau. The number in parenthesis indicates sample 
size of each population. The horizontal lines indicate sample range and the vertical 
lines sample mean. The black rectangles represent one standard deviation on each 
side of the mean; the white rectangles represent 2.646 standard errors on each side of 
the mean (Eberhardt, 1968). Dots represent specimens from the following inter- 
mediate localities outside the geographic range of the samples: 1, 2, Ventanas, 
Durango; 3, N of San Bias, Nayarit; 4, La Cumbre de los Arrastrados, Jalisco; 5, 7 mi 
S Rincon de Romos, Aguascalientes; 6, 7, Tacicuaro, Michoacan; 8, 10, Guanajuato, 
Guanajuato; 9, Mt. Cubilete, Guanajuato; 11, Jalapa, Veracruz; 12, Tuxpango, Vera- 
cruz; 13, San Diego, Puebla; 14, Quiotepec, Oaxaca. 
8 CONTRIBUTIONS IN SCIENCE NO. 179 
Specimens from population C in eastern Mexico have fewer ventral- 
subcaudal scales than specimens from B and in this character indicate a con- 
tinuation of a cline. The trend is continued within population C in that 
northern specimens have higher totals than do southern specimens. The highest 
counts (290, 300) are found in northern specimens from Tamaulipas, while 
the lowest counts (278, 277) are from snakes from more southern localities in 
San Luis Potosi and Hidalgo. 
Two specimens from Tacicuaro, Michoacan on the interior drainage of 
the Rio Grande de Morelia and three from the vicinity of Guanajuato, Guana- 
juato in the drainage of the Rio Lerma are situated between populations B and 
C. Four of these five specimens exhibit ventral-subcaudal counts that lie on or 
between the means for populations B and C, and thus reflect their intermediate 
geographic position (Fig. 2, Nos. 6-10). 
Specimens from population D have the lowest ventral-subcaudal counts 
and are from localities at the southern limit of the range. Most of these locali- 
ties lie within the Pacific drainage of the Rio Verde althought some are from 
localities in the Atlantic drainage of the Rio Papaloapan. These eastern speci- 
mens, when considered together with two other specimens from eastern locali- 
ties north of population D (Fig. 2, Nos. 11, 14), suggest a possible connection 
between samples C and D along the eastern edge of the Mexican Plateau. The 
specimen from Jalapa, Veracruz (Fig. 2, No. 11) and the type of Trimorpho- 
don tau from Quiotepec, Oaxaca (Fig. 2, No. 14) have ventral-subcaudal 
counts that are within the range of variation of population D but slightly higher 
than the average and thus approach populations C and F in this character. 
Snakes from the largest sample, population E, average about 13 more 
ventral-subcaudal scales than specimens in population D and, in this respect, 
are nearly identical to those in population C (Fig. 2). Sample C is located 
nearly 400 kilometers north of E and separated from it by the Balsas Basin and 
the Mexican Plateau. 
Population F averages slightly more ventral-subcaudal scales than E, but 
this difference is not significant at the 95 percent level. All known specimens in 
sample F are from localities in the upper Balsas Basin. The holotype of 
Trimorphodon collaris from western Veracruz (Fig.. 2, No. 12) and the holo- 
type of T. forbesi from southern Puebla (Fig. 2, No. 13) are both from locali- 
ties in eastern drainage systems. These two specimens have ventral-subcaudal 
counts similar to those of population F. Thus, specimens from southeastern 
Puebla and adjacent Oaxaca and from Veracruz have two patterns in the 
number of ventral-subcaudal counts. The holotypes of Trimorphodon collaris 
and T. forbesi (Fig. 2, Nos. 12, 13) are more similar to specimens from popu- 
lation F, while the holotype of T. tau and the Jalapa specimen (Fig. 2, Nos. 
11, 14) are more similar to snakes from population D. 
Snakes from population G have more ventral-subcaudal scales than are 
found in either E or F. In this respect sample G approaches sample B which 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 9 
lies immediately to the north. There is no significant difference (95 percent 
level) between samples B and G in the numbers of ventral-subcaudal scales. 
This analysis shows that there is a clinal trend in total ventral-subcaudal 
scales within population A and among populations A, B, C and D, with higher 
counts in the north and lower counts in the south. Populations E, F, and G 
are more closely related to each other than they are to either of the two 
geographically adjacent populations, B in the north and D in the south. How- 
ever, these three Balsas-Tepalcatepec Basin samples (E, F, G) have the same 
trend of higher totals in the north and lower totals in the south. In this instance, 
however, the trend is somewhat less marked. 
Anal scale.?The anal scale is divided in all specimens except one. A male 
from Morelos (TCWC 7390) has an entire anal scale. 
Loreal scales.?The number of loreal scales varies from two to five on 
each side of the head, with the majority of specimens having either two or 
three loreal scales (Table 1). Two loreals are more common in specimens from 
populations B, C and D, while three loreals are typical of populations A, E, F 
and G. 
Preocular scales.?Although preocular scales may vary in number from 
one to four, the majority of snakes in all populations have three (Table 1). 
Specimens with two preocular scales are found in all populations except D. A 
single preocular is present in one specimen from population F. 
Postocular scales.?Three postocular scales are characteristic of most 
specimens (Table 1). All snakes from sample F have three postoculars. Two 
postocular scales occasionally occur in the other six samples. Four scales are 
known only from specimens in populations A and E. 
Temporal scales.?Most specimens have either two or three primary 
temporals and three or four secondary temporals. The majority of specimens 
in populations A, E, F and G have three primary and four secondary temporal 
scales, while specimens from population B, C, and D usually have two primary 
and three secondary temporals (Table 1). The differences may reflect the 
smaller sample sizes of these populations. A single primary temporal occurs 
only once, in population B; five primary temporals occur only once, in popula- 
tion E. In five instances snakes from sample D have two secondary temporals. 
A comparison of the total number of lateral head scales (loreals, oculars 
and temporals) for the specimens from each sample shows that the higher 
numbers and means are characteristic of populations A (28-37, x = 30.9, 
N=23), E (26-39, x = 30.8, N = 48) and F (26-34, x = 31.2, N = 25), while 
the lower totals and means are found in samples B (23-31, x = 28.2, N=14), 
C (25-31, x = 27.9, N=12) and D (24-32, x = 28.2, N=20). Population G 
(24-32, x = 29.0, N=19) is somewhat intermediate in total head scales but is 
slightly closer to the lower than to the higher values. There is considerable 
variation in the number of head scales within some populations and some 
variation among several populations. We do not consider the different head 
10 CONTRIBUTIONS IN SCIENCE NO. 179 
scale characteristics to be of systematic importance in distinguishing any of 
the samples. 
Labial scales.?Most snakes have either eight or nine supralabials, except 
in population C where all specimens have eight (Table 1). Eight is the more 
common number of supralabials in all populations except F, in which nine 
occurs more frequently. Only in sample D are specimens with seven supra- 
labials found. The type specimen of Trimorphodon tau has six supralabials on 
each side, the lowest number known. 
Although the fourth and fifth supralabials border the eye in the majority 
of specimens examined, some variation was noted. In populations A, D, E, and 
F occasional individuals have the fifth and sixth supralabial bordering the eye. 
One specimen from each of populations F and G has the third, fourth and fifth 
supralabials bordering the eye on one side while the fourth and fifth border the 
eye on the other. The fifth supralabial borders the eye on one side in two 
specimens from population F; the usual condition is found on the other side. 
There is considerable variation in the number of infralabials from popu- 
lation to population and within populations (Table 1). Twelve is the most 
common number, although ten, eleven, and thirteen infralabials are found in 
nearly all samples. Population D has the lowest recorded number of infra- 
labials (nine) and has a lower mean than do the other six samples. 
The small gular scales usually separate the infralabial series from the chin 
shields at the level of the fifth or sixth infralabial scale. In population A this 
separation occurs in the majority of snakes at infralabial six. In population D 
this separation occurs in most specimens at infralabial five. In the other five 
populations the separation occurs about equally at the fifth or sixth infra- 
labial. Occasionally the infralabial series may be separated from the chin 
shields at a level as far anterior as the fourth infralabial or as far posterior as 
the seventh. 
Dorsal scales.?The dorsal scales of Trimorphodon are smooth, with 
paired apical pits. The scales are arranged in diagonal rows and vary con- 
siderably in number. The anterior count at one head length behind the head 
ranges from 21-27 rows; 75 percent of the individuals have 22, 23, or 24 
rows. The number of scale rows at midbody varies from 17-25; 80 percent of 
the snakes have 22 or 23 rows. At one head length in front of the vent, there 
are between 14 and 18 rows, and at this level 83.33 percent of the sample have 
15 or 16 rows. 
The reduction in scale rows is similar to the reduction found in Lepto- 
deira (Duellman, 1958:20). The reduction involves changes in the para- 
vertebral row. The level (ventral scale) at which reduction in scale rows take 
place is highly variable with no geographic consistency. 
PATTERN AND COLORATION 
Cross bands.?The number of dorsal body bands (body and tail blotches) 
in individuals with complete tails ranges from 18-46, though evidence suggests 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 11 
TABLE 1. 
Range and Percent Distribution of Various Head Scales in 
the Seven Populations of Trimorphodon 
A B            C D E             F G 
No. of specimens           23 15            14 20 51 25 19 
2 6.5% 66.6%     75.0%    60.0% 18.07. 12.0% 44.7% 
3 87.0 33.4 25.0 35.0 79.0 86.0 55.3 
Loreals               4           6.5                  5.0          2.0          2.0   
5                     1.0     
2            6.5 13.3         14.3            8.9          2.0 15.8 
Preoculars          3         93.5 83.3        85.7 97.5 88.1 90.0 84.2 
4   3.4   2.5 3.0 6.0 
2          19.2 3.5         10.7 7.5           1.9         ? 10.5 
Postoculars         3          76.6 96.5        89.3 92.5 94.1 100.0 89.5 
4 4.2       4.0     
1   3.5           
2 19.6 55.2 39.3 60.0 23.5 24.0 31.6 
Primary 3 78.3 41.3 57.2 37.5 71.6 74.0 68.4 
Temporals          4         21.0 ?          3.5 2.5          4.0          2.0   
2                            12.5                         ? 
Secondary           3 26.1 44.8 63.0 50.0 25.7 12.0 47.4 
Temporals          4 60.9 55.2 37.0 35.0 72.3 86.0 52.6 
5 |3.o                   2.5 2.0 2.0 
7                            ? 10.0                            
8 60.9 69.0 100.0 72.5 63.9 39.5 57.9 
Supralabials       9 37.0 31.0          15.0 29.9 58.1 39.5 
10 2.1          ?          2.5 6.2 2.4 2.6 
9                           2.5                          
10 2.1 3.3 9.5 27.5 2.1 4.6 ? 
11 28.4 30.0 28.6 50.0 14.9 23.3 26.5 
Infralabials       12 47.8 43.4 47.6 20.0 45.8 44.2 44.1 
13 21.7 20.0 14.3 35.1 25.6 20.6 
14           3.3 ?          2.1 2.3 8.8 
12 CONTRIBUTIONS IN SCIENCE No. 179 
that higher numbers do occur (see below). The higher values are found in 
samples A, B, C and D while the lower numbers are characteristic of the three 
Balsas-Tepalcatepec Basin populations, E, F and G. The numbers of body 
bands for the seven populations and for geographically intermediate specimens 
are shown in Figure 3. 
There is a decrease of dorsal body bands within population A from north 
to south. Specimens from Sonora have 27-36, x = 32 (N = ll); specimens 
from northern Sinaloa have 29-33, x = 30 (N=14); specimens from central 
Sinaloa have 25-31, x = 28 (N=10). Snakes from population B on the aver- 
age have more body bands than specimens from population A, and snakes of 
population C tend to have more bands than those from B. Specimens that are 
geographically intermediate between samples A and B have an intermediate 
number of bands. The same is true for two specimens from the area between 
samples B and C (Fig. 3, Nos. 8, 9). 
In population C the Hidalgo specimens apparently have more bands than 
A 
B 
C - 
D - 
E - 
F - 
G - 
_ 
(25) 
-    (15) 
8,9 7,10 
oi: 
(20) 
(44) 
(25) 
(19) 
12 11,13,14 
~\? 
15 20 25 30 ?J? 45 35 40 50 
Figure 3. Statistical analysis of the number of cross bands in populations A through 
G of Trimorphodon tau. See legend to Figure 2 for explanation of diagrams and 
symbols. 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 13 
do the Tamaulipas specimens. The only Hidalgo specimen with a complete tail 
has 43 body bands. Three other snakes from Hidalgo appear to have 40, 42 
and 49 bands or more. These three specimens have damaged tails and, for this 
reason, are not included in Figure 3. The higher number of bands indicated 
for southern specimens in population C may account for the high numbers 
found in two of the intermediate specimens between B and C (Fig. 3, Nos. 7, 
10). Both of these specimens (FMNH 105193, USNM 11370) are from 
localities slightly farther south than most of the localities in either B or C. 
Specimens from population D, like population B, have fewer dorsal 
blotches than those from population C. Three of the four snakes from locali- 
ties intermediate between C and D in eastern Mexico are more similar to D 
than to C. The fourth snake (Fig. 3, No. 12), the holotype of Trimorphodon 
collaris, is much closer in band number to specimens from sample F. 
Snakes from populations E and F average 11 to 13 fewer blotches than 
specimens from population D, the sample that is closest geographically. They 
are most similar to snakes from population A which is the farthest removed 
geographically. In band count, samples E and F are most similar to sample G. 
These populations (E, F, G) are significantly different from all of the other 
populations. Although populations B and G are in close geographic proximity, 
there is no overlap in the number of body bands. In fact these two samples are 
separated by a mean difference of 15 dorsal body bands. 
The lengths of the bands may vary considerably on a single individual and 
among individuals of the same or different populations. In order to evaluate 
the differences in band size, the lengths on the middorsal scale row (as indi- 
cated by the number of included scales) of three band-interspace-band se- 
quences were compared. The first sequence behind the collar (anterior), a mid- 
body sequence, and the last sequence befor the vent (posterior) were used. 
These values are presented in Table 2. 
In all populations the first dark cross band usually is the longest. The 
second cross band is longer on the average than either of the midbody bands, 
and they, in turn, always average longer than the posterior body bands. The 
mean band length of specimens from population A is greater than that of 
specimens from B, and mean band length in B is greater than in C (Table 2). 
In all instances the bands on snakes from population D average longer than 
bands in C but are shorter than bands on snakes in B. 
Bands of specimens from populations E, F and G average longer than 
those of any of the other four samples. The only exception is the mean first 
band length of sample A which is longer than in sample E but never as long 
as in samples F or G. In general, specimens from population G have longer 
bands than specimens from F, and specimens from F have longer bands than 
specimens from E. The longest mean band lengths at all three body positions 
are characteristic of specimens from population G while the shortest band 
lengths are always found in population C. 
14 CONTRIBUTIONS IN SCIENCE NO. 179 
l-i 
o 
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00 p^ JL q>oqqqoqqq 
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a r? cK        N'        ^        ^        ~        ^        ^        ^        ^- 
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JD .S3 
<ZHWDi^Ooi     ^MQIUOQ^     feO^HW^^Ofti 
0 CD 
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1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 15 
There is an average decrease in interspace length from anterior to 
posterior in all samples except F and G. In the former the midbody interspaces 
average shorter than the posterior interspaces while in the latter the midbody 
interspaces average slightly longer than either the anterior or posterior inter- 
spaces which are the same (Table 2). Specimens from populations A and B 
have the smallest mean interspace lengths. Specimens from population F have 
the longest interspace lengths. 
There is no consistent number or location of bands which show signs of 
splitting or fusion (indicated by light centers) in any population. However, 
there is some consistency within certain populations in the extent of the light 
central area. For example, in Oaxaca the light areas within the darker bands 
are relatively large and diffuse. In Sinaloa the central light areas often form 
discrete spots. 
Collar length.?The length of the light nuchal collar varies among indi- 
viduals from the same population. In some specimens the first body blotch 
contacts the posterior margin of the head cap or the parietal scales on the 
midline or is separated from them by only half a dorsal scale. Others may have 
A 
B H 
C 
D - 
E - 
F 
G -I 
(24) 
(15) 
(14) 
(20) 
(49) 
(24) 
(18) 
I 3 2.4 
6 5,7,10 0 
? ? ?? 
11,14 13 12 
0 3 
r 
4 6 
Figure 4. Statistical analysis of the collar lengths in populations A through G of 
Trimorphodon tau. See legend to Figure 2 for explanation of diagrams and symbols. 
16 CONTRIBUTIONS IN SCIENCE NO. 179 
as many as six dorsal scales separating the first body blotch from the head cap 
or the parietal scales. However, the collars among the seven samples have 
nearly the same average lengths as indicated by the number of light scales on 
the midline (Fig. 4). Only population F has a noticeably higher number of 
dorsal scales in the nuchal collar. In addition, snakes from population F have 
the greatest interspace length (Table 2). Most of the specimens from inter- 
mediate localities have intermediate collar lengths which fall within the range 
of variation of the two samples concerned. Notable exceptions, however, are 
the collar lengths for the type specimens of T. collaris and T. forbesi which are 
plotted between populations C and D (Fig. 4, Nos. 12, 13). Both of these have 
collar lengths most similar to those characteristic of sample F. The type of 
Trimorphodon forbesi has four scales, very near the mean for F, while the 
type of T. collaris has five and is near the upper end of the range of sample F. 
Dorsal head cap.?The pattern of dark and light colors on the head 
generally is consistent within a geographic area. Because of this geographic 
consistency, a detailed analysis of the head patterns is extremely useful in 
determining the relationships among the seven samples. Although individual 
head patterns may be very complex (Figs. 5, 6), they can be analyzed in terms 
of the following components: snout?light or dark rostral and internasal 
scales; presence or absence of a prefrontal bar?light bar extending across the 
prefrontal scales with dark anterior and posterior borders; presence or absence 
of an interocular (interorbital) bar?a light bar extending between the eyes, 
usually including the supraocular scales and the frontal scale; presence or 
absence of a parietal mark?a light mark of various design that may or may 
not connect to the interorbital bar or the light collar; presence or absence of an 
occipital spot?a medial, dark rounded spot located on the posterior portion 
of each parietal scale and the adjacent dorsal scales in the collar; posterior 
border?the shape of the posterior margin of the dark cap where it is bordered 
by the light nuchal collar. 
Most snakes from population A have dark snouts (a few specimens from 
near Alamos, Sonora have light snouts) and a light prefrontal bar (blending 
into the snout of the light snouted forms) that is restricted to the anterior third 
of the prefrontal scales (Fig. 5A). Occasionally (three specimens) the pre- 
frontal bar is connected with the interorbital bar by a straight or irregular 
medial area. The interocular bar is always present, usually has irregular bor- 
ders, and generally is continuous between the orbits (interrupted in two speci- 
mens). A parietal mark is always present but extremely variable in shape and 
extent (Fig. 7). Frequently the parietal mark is shaped like an irregular-armed 
trident, a bell, a teardrop, or consists of two oblong parts arranged at right 
angles to form an inverted T. The parietal mark (connected medially to the 
interorbital bar in one specimen) begins at the posterior edge of the frontal 
scale and continue posteriorly to connect with the collar (56 percent). In the 
remaining specimens the parietal mark is separated from the light collar. An 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 17 
occipital spot is present in 12 of the 14 specimens with the parietal mark-collar 
connection. The posterior border of the head cap may have a single median 
indentation (16 specimens), a lateral indentation on either side of a median 
posterior extension (five specimens), or it may be nearly straight (three 
specimens). 
The two specimens from Ventanas, Durango have complete interorbital 
Figure 5. Representative dorsal head cap patterns for specimens of Trimorphodon 
tau from A) Terreros, Sinaloa in population A; B) between Hostotipaquillo and 
Magdalena, Jalisco in population B; C) S Ciudad Victoria, Tamaulipas in population 
C; D) intermediate locality at Jalapa, Veracruz. 
18 CONTRIBUTIONS IN SCIENCE NO. 179 
bars and light snouts that include the area of the prefrontal bar (Fig. 7). The 
simple parietal marks are restricted to the suture lines between the parietal 
scales. The parietal mark is connected to the light collar in one specimen and 
separated in the other. An occipital spot is present in the snake with the 
parietal mark-collar connection. 
The specimen from near San Bias, Nayarit has a dark snout, a prefrontal 
bar, an interorbital bar, a parietal mark connected to the collar, and an occipital 
spot. It is very similar to several Sinaloan specimens. 
Most snakes from population B have dark snouts (light in the Zacatecas 
specimen and two Michoacan specimens) and distinct light prefrontal bars 
(66 percent of individuals). The interorbital bar is present (faint in KU 67735) 
and complete in all specimens except one (UMMZ 118950), where it is inter- 
rupted medially. The arms of the parietal mark, which is usually Y-shaped, 
edge the frontal scale posteriorly (Fig. 5B; Cope, 1900: fig. 315). The upright 
base extending posteriorly along the parietal suture may connect to the collar 
(six specimens) or remain separate from it (five specimens). In one specimen 
(FMNH 105194) the arms of the parietal mark connect with the interorbital 
bar on the supraocular scales forming a triangle (Taylor, 1939: pi. 35, fig. 2). 
The parietal mark is oblong in three snakes and heart-shaped in one. The 
occipital spot is less common than in population A, being found in only two 
specimens. The posterior border of the head cap is rounded in two specimens, 
forms a straight edge in one, is indented medially in five, and has a medial 
posterior projection in the remaining seven snakes. 
A snake from La Cumbre, a locality southwest of population B, has a head 
pattern very similar to many specimens from B in that it has an interocular bar 
and a medial posterior projection of the head cap. The snout is somewhat 
lighter than the rest of the head cap and includes the prefrontal bar. The 
parietal mark is V-shaped and outlines the frontal scale posteriorly. 
Two specimens from Tacicuaro, Michoacan (southeast of population B) 
have dark snouts, interorbital bars, and irregular Y-shaped parietal marks that 
connect to the light collar. An occipital spot is present in one specimen but 
absent from the other (Fig. 7). Although these two snakes lack prefrontal bars, 
they are similar in head pattern to other snakes from population B. 
Three specimens from Guanajuato (east of population B) have inter- 
ocular bars and Y-shaped parietal marks characteristic of most specimens from 
B but resemble the Tacicuaro specimens in lacking the prefrontal bars. The 
parietal mark connects to the collar in two specimens and is separate from it 
in the third. The snout, including the prefrontal bar, is light in one specimen 
and dark in two. 
An Aguascalientes specimen from a locality north of population B has a 
light snout that includes the prefrontal. In this respect the Aguascalientes snake 
is similar to one of the Guanajuato specimens and to the Zacatecas specimen 
in population B. The interorbital bar is complete and the parietal mark, which 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 19 
is roughly Y-shaped, does not connect to the light collar. The posterior border 
of the head cap is rounded. 
Specimens from sample C have a very complex head pattern. Half of 
the individuals examined have a light snout that encompasses the prefrontal 
area. The other specimens have a dark snout with either a well-developed or 
very faint prefrontal bar. Many specimens, especially those with the lighter 
snout have a patch of dark color in the center of each prefrontal scale. These 
patches may be joined medially or separated by a lighter suture line between 
the prefrontal scales. About half of the specimens have a second light bar on 
the posterior edges of the prefrontals. The interocular bar is always present and 
usually expanded on the frontal scale. In one-third of the specimens the inter- 
orbital bar is connected anteriorly to the prefrontal bars and posteriorly to the 
parietal mark. In these specimens the dark head color actually is restricted to 
six spots, one in the center of each prefrontal scale, one at the anterior edge of 
each supraocular and adjacent frontal scale, and one on the posterior part of 
each supraocular and adjoining frontal and parietal scales. 
In most of the specimens from Tamaulipas and San Luis Potosi, the arms 
of the parietal mark form a V and outline the posterior edges of the frontal 
scale. The posterior part of the parietal mark bifurcates and encloses a large 
occipital spot before joining the collar (Fig. 5C). In these specimens the 
posterior border of the head cap is indented medially. 
The parietal marks of the four specimens from Hidalgo differ from the 
more northern representatives of sample C. One specimen (LACM 53023) has 
a Y-shaped mark outlining the frontal edges and connecting to the collar. It 
lacks an occipital spot and has a postero-medially indented head cap. In two 
other specimens (AMNH 93432 and ANSP 14770) the parietal mark is lyre- 
shaped and not connected to the light collar. The arms of the lyre extend to the 
frontal borders, connecting with the interorbital bar on one side in one speci- 
men. They do not outline the postero-medial edges of the frontal scale. In both 
specimens the occipital spot is incorporated into the head cap, thereby extend- 
ing the posterior border of the cap medially. In the fourth specimen (USNM 
110401) the interocular bar extends posteriorly to the tip of the frontal scale. 
The parietal mark is fragmented into three parts. On the left side the mark 
borders the frontal anteriorly and extends posteriorly nearly to the light collar 
forming a shallow, laterally concave arc. On the right side only the anterior 
half of the arc is present. The posterior half consists of a light rounded spot on 
the posterior part of the right parietal scale, just above the light collar. The 
posterior border of the head collar is nearly straight medially but rounded 
laterally. 
A specimen from Jalapa, Veracruz has a light snout extending over the 
anterior half of the prefrontals. Each nasal scale is very faintly pigmented. The 
interorbital bar is complete and connects medially to the light snout along the 
prefrontal suture. The parietal mark is irregular in shape, restricted to the 
20 CONTRIBUTIONS IN SCIENCE NO. 179 
parietal suture (Fig. 5D) and connected to the light collar. The occipital spot 
is well defined. 
The type specimen of Trimorphodon collaris lacks pigment on the inter- 
nasal scales. Its interocular bar is broken about the middle of each supraocular, 
and it has a more rectangular-shaped parietal mark connected to the collar. In 
other respects it is very similar to the Jalapa specimen. 
The type specimens of Trimorphodon tau and T. forbesi also are from 
localities in the Atlantic versant and generally are similar to the two specimens 
mentioned above. The type of T. tau has dark circular marks in the center of 
each internasal scale. The light snout is connected medially and laterally with 
the prefrontal bar which is also connected with the complete interocular bar 
along the suture between the prefrontals. The lighter color of the collar con- 
tinues onto the temporal parts of the head connecting with the postero-lateral 
portions of the interocular bar. As a result, the dark parietal portion of the 
head cap is greatly restricted and completely surrounded by the lighter colora- 
tion. The parietal mark is connected to the collar. Posteriorly the head cap is 
nearly straight. The occipital spot is present but small. The type of T. forbesi 
also has a lighter snout that includes the prefrontal area. The interocular bar is 
complete and connects along the prefrontal suture to the lighter snout. The 
parietal mark is rounded and broadly joined to the light collar. The occipital 
spot is small. The posterior border of the head cap is rounded laterally and in- 
dented medially. In general these four specimens from eastern Mexico (Vera- 
cruz, Puebla, Oaxaca) are very similar in overall head pattern. 
The head patterns of specimens from population D generally are more 
uniform than are those from population C. Most of the specimens (75 per- 
cent) have a dark snout and lack a prefrontal bar. Two of the five individuals 
with a light snout have dark pigment in the central parts of the internasal 
scales and a suggestion of a prefrontal bar. In this respect they are similar to the 
type of Trimorphodon tau. In several specimens, including light-snouted and 
dark-snouted individuals, the edges of the internasal and prefrontal scales are 
lighter than the central portions (Fig. 6A). Ten specimens have a light bar 
along the suture between the prefrontals. Often this bar is connected to the 
interocular bar (50 percent) forming the inverted T-pattern characteristic of 
Trimorphodon tau (Cope, 1869: 152). The interocular bar is always present 
and frequently (50 percent) extends laterally to the orbits. In some specimens 
(eight of 20) the interocular bar forms a shallow arc, concave posteriorly. 
The parietal mark has a simple configuration, rarely touching the frontal scale, 
and is connected with the light collar in all but two specimens (Taylor, 1940: 
fig. 8). In one specimen (AMNH 10093) the mark is irregular in shape (two 
lateral arms on each side) and contacts the posterior part of the frontal scale. 
An occipital spot is present in only five specimens. 
The head cap is indented medially in all but two specimens from sample 
D. In these two specimens the parietal mark and the collar do not connect, and 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 21 
thus the head cap extends postero-medially. The white collar extends anteriorly 
along the sides of the head in these specimens, together with 16 of the 18 
indented head cap forms, giving the head cap a rounded appearance. In two 
(Fig. 7) the postero-lateral edges of the cap are nearly straight. 
We examined the head patterns of 48 snakes from population E. In only 
eight of these does the light snout include the prefrontal bar area. Although the 
Figure 6. Representative dorsal head cap patterns for specimens of Trimorphodon 
tau from A) 3 mi NE Mitla, Oaxaca in population D; B) Chilpancingo, Guerrero in 
population E; C) Coalcoman, Michoacan in population G; D) 4 mi S Autlan, Jalisco 
in population G. 
22 CONTRIBUTIONS IN SCIENCE NO. 179 
snout in these few specimens is somewhat lighter than the rest of the cap, it is 
still well pigmented and not the white or very light tan characteristic of certain 
light-snouted specimens from populations A and C. None have a defined pre- 
frontal bar, although three individuals have a pair of light spots on the anterior 
prefrontal scales. Three other specimens have a medial light spot on the pre- 
frontal suture. An interorbital bar is lacking in 23 specimens, reduced to a 
median frontal spot or to two lateral supraocular spots in 21 specimens, and 
complete in four specimens. None has a connection between the interorbital 
bar and parietal mark. In all specimens, except four, the parietal mark is con- 
nected to the light collar (Fig. 6B) or is absent. Of these four, two have a small 
circular spot on the parietal suture, one has a small central and two small lateral 
spots, and the fourth has two lateral spots that appear to be remnants of a V- 
shaped mark. Of the remaining 44 specimens, eight have no indication of a 
parietal mark; the posterior margins of their head caps are rounded laterally 
(Fig. 7). Most of the others have a median extension of the collar connecting 
to the parietal mark. Usually the parietal mark or anterior end of the collar 
extension is rounded, but occasionally it may be Y- or V-shaped or may narrow 
rapidly at its anterior apex near the frontal scale. Occasionally (six specimens) 
the collar has a double extension onto the parietal region, and the head cap 
extends posteriorly on the midline. The head cap is rounded laterally in nearly 
all of these specimens. An occipital spot is present in only nine. 
In twelve of 24 specimens from sample F, the snout is lighter than the 
rest of the head cap and includes the prefrontal bar area. In this respect they 
are similar to the light-snouted individuals of population E. Only two of the 
dark snouted specimens have a prefrontal bar. When a complete interorbital 
bar is present (three specimens), it is faint. In twelve other snakes, the bar is 
fragmented or reduced to one, two, or three circular spots or short bars. There 
is not interorbital bar in nine specimens (Taylor, 1940: pi. 52). Four specimens 
lack parietal marks and have a head cap with a rounded posterior margin. 
Three specimens have shallow V-shaped parietal marks that outline the frontal 
scale and are not connected with the light collar. In these specimens the 
posterior edge of the head cap has a single medial indentation, two lateral 
indentations, or a postero-medial extension. In the remaining snakes (17) the 
parietal mark is connected to the collar, and thereby, the posterior edge of the 
head cap is indented medially. The extended collar-parietal mark may be 
broadly Y-shaped (Fig. 7), triangular, narrow and restricted to the parietal 
suture, or wishbone-shaped. There is a large distinct occipital spot in the collar 
extension in most (12 of 17) of these specimens. 
The head patterns are remarkably consistent in population G. None, ex- 
cept the type of T. fasciolata, have a light snout or show any trace of a pre- 
frontal bar. In the type specimen of T. fasciolata the snout and the edges of the 
prefrontal scales are somewhat lighter than the rest of the head cap. An inter- 
orbital bar is lacking in all specimens (Fig. 6C) except three. In two of these 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 23 
(UMMZ 112516 and the type of T. fasciolata) the supraocular scales have 
light centers. The third specimen from Autlan, Jalisco (KU 27191) has two 
light circular spots in the interorbital area. Distinct parietal marks are lacking 
from all except the Autlan specimen (Fig. 6D) and a specimen from near 
Apatzingan (UMMZ 112515). In the latter there are two small spots on the 
posterior third of each parietal scale. The posterior margin of the head cap is 
indented in one specimen from Apatzingan (FMNH 37079) and the type of 
T. fasciolata and shallowly indented in a third (UMMZ 104696). Occipital 
spots, lacking in other specimens, are present in these three snakes. The 
posterior margin of the head cap is doubly indented in nine specimens (Fig. 
6C), rounded in four, nearly straight in two, and slightly convex in one. 
The geographic distribution of the different head patterns is illustrated 
in Figure 7. 
Coloration.?These snakes have considerable variation in coloration from 
sample to sample and within some samples. Because adequate color descrip- 
tions and pictures of specimens from many areas are available in the literature 
(Taylor, 1939: 364-367; 1940: 474-479; Smith, 1941: 161-167; Peters, 1954: 
33; Davis and Dixon, 1957: 24; Duellman, 1961:  111; Brown and Brown, 
Figure 7. Geographic distribution of representative head cap patterns for specimens 
of Trimorphodon tau from localities within the seven samples and selected inter- 
mediate localities. 
24 CONTRIBUTIONS IN SCIENCE NO. 179 
1967: 325), no detailed color description will be included here. Instead we 
will summarize this information and present it together with color notes on 
living specimens from Sinaloa and Puebla. 
The ground color of adults ranges from various shades of brown to fawn, 
pale tan or gray, usually becoming darker posteriorly. Juveniles often have a 
more reddish or grayish ground color than do the adults. The cross bands of 
both age groups are darker than the ground color and often yellow-brown or 
gray-brown to black. In many specimens the center of each band is lighter. The 
edges of each band are usually bordered with dark brown or black. Juveniles 
apparently have darker bands than adults from the same area. Laterally, 
smaller dark blotches are present in the interspaces of some specimens. The 
head cap is brown, gray-brown or black and nearly the same color as the cross 
bands. The lips, chin and throat usually are tan or white. The venter may be 
tan or creamy white, and often with a reddish or salmon tinge posteriorly. In 
some snakes the venter is mottled by ventral extensions of the cross bands and 
interspace blotches; in others the venter may be spotted. Some have a nearly 
immaculate belly. In some juveniles the ventral surface of the tail may be 
nearly black. 
The iris may be yellow-brown, gray-brown or grayish-tan. 
DISCUSSION 
CHARACTER ANALYSIS 
Much similarity exists among the seven samples. Some characters indicate 
independent, discordant patterns of variation. Even though most characters are 
not diagnostic, three are particularly useful in deducing the relationships among 
the seven samples: number of ventral plus subcaudal scales, number of dorsal 
body bands, and dorsal head cap pattern. 
The number of ventral-subcaudal scales decreases from north to south in 
samples A through C. The trend continues southward into population D, where 
the lowest counts are recorded. Two specimens (Fig. 2, Nos. 11, 14) from 
intermediate areas between C and D are more similar to D than to C in this 
character, while two other specimens from intermediate areas (Fig. 2, Nos. 
12, 13) are more similar to C and F than they are to D. This suggests a con- 
nection among the samples through the high river valleys of southeastern 
Puebla and Oaxaca. Population G has the highest counts and is the most 
northern of the three Balsas-Tepalcatepec Basin samples. In this character 
sample G approached sample B, its closest geographic neighbor. The ventral- 
subcaudal scale counts will not allow for absolute distinction between speci- 
mens from geographically adjacent samples. 
An analysis of the number of dorsal cross bands (Fig. 3) gives a slightly 
different picture of the relationships among the seven samples. Among popula- 
tions A, B, and C there is an increase in number of dorsal blotches from north- 
west to southeast. The geographically intermediate specimens generally con- 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 25 
firm this trend. Sample D has fewer bands than does C and thus has a slightly 
different relationship to A, B, and C in this character than it did in terms of 
ventral-subcaudal scales. In this respect, however, the number of dorsal 
blotches of sample D approaches those characteristic of samples E and F. Of 
the four specimens from eastern Mexico that are geographically intermediate 
among samples C, D and F, three (Fig. 3, Nos. 11, 13, 14) have counts most 
similar to the counts of D while the fourth (Fig. 3, No. 12) has a count most 
like those of sample F. 
In dorsal cross bands E, F and G are closely related to each other and 
well differentiated from sample D. The most striking thing about the dorsal 
band counts is the difference between samples G and B which do not approach 
each other even though the two populations are closely adjacent (Fig. 3). This 
is a notable exception to their similarity in the number of ventral-subcaudal 
scales. 
The same general relationship is present in the seven samples for both 
dorsal head patterns and dorsal cross bands. An interocular bar, usually com- 
plete, and a discrete parietal mark are always present in specimens from 
samples A, B, C, and D. The remnants of an interocular bar are present in 43 
of 91 specimens from samples E, F and G. Only seven specimens from the 
Balsas-Tepalcatepec samples have a complete interocular bar. A discrete parie- 
tal mark, that is one not connected to the collar, is found only in nine of the 
91 specimens in samples E, F and G. A prefrontal bar or light snout including 
the area of the prefrontal bar is found in most snakes from samples A, B and C. 
In sample D a prefrontal bar is usually lacking, as it is in most specimens from 
samples E and G. Approximately 50 percent of the specimens from sample F 
have light snouts that include the area of the prefrontal bar and thus are some- 
what intermediate between samples A, B, C and D, E, G. 
In summary, the Balsas-Tepalcatepec Basin samples (E, F and G) have 
a darker, more uniform head cap than is found in specimens from samples A, 
B, C and D. The Balsas-Tepalcatepec samples generally lack the prefrontal and 
interocular bars and the discrete parietal marks characteristic of the other 
samples. In general they lack the ornate head marking characteristic of the 
other four populations. Except for two snakes (KU 27191 and USNM 
110400), there is no indication of any similarity between samples B and G in 
characters of head pattern. Some specimens from samples E and F show an 
apparent relationship to samples C and D by possessing remnants of an inter- 
ocular bar and parietal mark. The head patterns of specimens from areas geo- 
graphically intermediate between samples A, B, C and D have intermediate 
head patterns. 
TYPE SPECIMENS 
It seems appropriate to discuss briefly the six type specimens with refer- 
ence to our seven populations to clarify our systematic treatment of the various 
samples. 
26 CONTRIBUTIONS IN SCIENCE NO. 179 
The type specimen of Trimorphodon tau is a small snake in relatively poor 
condition. It was adequately described by Cope (1869) and redescribed by 
Taylor (1939). Although from a locality northwest of sample D, in all char- 
acteristics, it is typical of specimens from that sample. 
The holotype of Trimorphodon upsilon is typical in all respects of speci- 
mens from sample B and was included in that unit. Zweifel (1959) noted that 
many of the specimens collected by Major probably did not come from 
Guadalajara, Jalisco as the locality information indicated but possibly were 
from Colima. However, Zweifel did point out that the type of Trimorphodon 
upsilon may actually have been from Guadalajara as additional specimens of 
this species are known from the same general area. Our analysis supports 
Zweifel's contention that Guadalajara probably is the type locality as originally 
stated. 
The cotypes of Trimorphodon latifascia from Puebla have the character- 
istics typical of Puebla specimens from sample F. However, they were not 
included in sample F because the specific type locality is unknown (Peters, 
1869). 
For purposes of nomenclatural stability and in accord with Article 74, 
International Commission on Zoological Nomenclature (1964), we designate 
ZMB 6652a, the larger of the two syntypes (588 mm total length), as the 
lectotype. The smaller specimen (417 mm total length), ZMB 6652b, is desig- 
nated the paralectotype in accord with recommendation 74E. Both specimens 
are males and have 211, 209 ventrals, 79, 74 subcaudals, and 21, 22 dorsal body 
bands. The snout is slightly lighter than the head cap in both specimens. In one 
the interocular bar consists of two short lateral spots and in the other of a 
median spot. The posterior border of the head cap is indented medially and 
rounded laterally in both. A faint occipital spot is present in the smaller 
paralectotype. 
The holotype of Trimorphodon collaris, like the type of T. tau, is a 
juvenile. Cope's description (1875) is accurate for the characters listed. Some 
confusion exists concerning the type locality and number of specimens (see 
Historical Review and Smith, 1941: 166). This specimen, although from a 
locality somewhat intermediate among samples C, D and F, is typical of speci- 
mens from sample F in the important characteristics of ventral plus subcaudal 
scales, collar length, and number of dorsal blotches. The band-interspace-band 
lengths also are closest to those characteristic of sample F. The head pattern is 
similar to the patterns found on specimens from both D and F, although it is 
more similar to those from D. We consider the specimen to be most similar to 
snakes from sample F. 
The type specimen of Trimorphodon fasciolata is a large male collected 
from a locality on the northeastern periphery of sample G. The specimen was 
adequately described by Smith (1941: 160-162). In all characteristics except 
certain details of head pattern (see previous description), it is typical of rep- 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 27 
resentatives of sample G, in which it was included. These differences in head 
pattern emphasize the marginal nature of the locality and may reflect its 
proximity to specimens from sample B and the intermediate specimens from 
Tacicuaro, Michoacan. 
Finally, the type of Trimorphodon forbesi is an exceptionally large male 
that is relatively well preserved but badly faded. In general our findings, on 
examination of the type, agree well with Smith's description (1941: 163-165) 
with two exceptions. We recorded five more ventrals and two more subcaudals 
than listed in the type description. Unfortunately the ventral scales are dam- 
aged in some areas and accurate counts are difficult to make. This may account 
for the discrepancies. However, we believe our count of 297 scales to be 
accurate. 
The other point with which we disagree is Smith's (1941: 164-165) dis- 
cussion of and reference to the "pattern reversal" characteristic of Trimorpho- 
don forbesi. It is quite obvious that this specimen is faded; apparently the brown 
color of the head pattern faded more rapidly than did the dark borders along 
the interocular bar and nuchal collar, thus giving the appearance of a light head 
pattern with a darker interocular bar and nuchal collar. We cannot accept the 
contention that this is anything other than a badly faded but originally nor- 
mally colored head pattern. The pattern itself is similar to the pattern of the 
type of Trimorphodon tau and other specimens in sample D. 
The remaining characters of forbesi that Smith (1941: 165) used to dis- 
tinguish it from other species include a divided anterior loreal, the fifth and 
sixth labials entering the eye, a faintly marked belly and white subcaudal sur- 
face, the number of cross bands, the narrow black borders of the cross bands, 
and the length of the cross bands on the mid-dorsal line. All of these charac- 
teristics are known from other samples (see previous description of geographic 
variation) and therefore are of little value in distinguishing this specimen. In 
ventral-subcaudal scales and collar length this specimen is more similar to 
sample F. In number of dorsal blotches and in head pattern, it is more similar 
to sample D. Certain characteristics of head scales and blotch length are inter- 
mediate between those for samples D and F. 
Thus, the type of Trimorphodon forbesi has some characters typical of 
specimens from sample D, some typical of specimens from sample F, and 
some that are intermediate. Because of its intermediate locality and character- 
istics, we consider the specimen to represent a population of Trimorphodon 
that apparently bridges the gap between samples D and F. 
In order to evaluate the usefulness of the three characters, ventral-sub- 
caudal scales, body bands and head cap pattern, as indications of phylogenetic 
relationship, we attempted to correlate their geographic variation with various 
environmental parameters. Klauber (1941) showed that desert specimens con- 
sistently tend to have more ventral scales than coastal specimens of the same 
species. He also found that specimens of Trimorphodon vandenburghi from 
28 CONTRIBUTIONS IN SCIENCE NO. 179 
the desert had more dorsal blotches than those along the coast. Klauber at- 
tributed these disparities to differences in humidity, and possibly temperature. 
Fox (1948) showed how different temperature regimes can influence scutella- 
tion in developing embryos of Thamnophis. Gravid females from the same 
natural population kept at cooler temperatures give birth to young with 
significantly fewer ventral and subcaudal scales than young from females 
maintained at warmer temperatures. Stebbins (1949) suggested that physical 
factors of humidity, temperature and light are important considerations deter- 
mining the coloration and pattern of the salamander Ensatina. 
In our analysis we could find no consistent correlation between environ- 
mental factors of temperature, rainfall or elevation and the geographic varia- 
tion in ventral-subcaudal scales, dorsal cross bands or head pattern. In some 
samples there appeared to be a positive correlation between ventral-subcaudal 
scales and temperature; in other samples the same character indicated an 
inverse relationship to mean temperature. These same results generally were 
found in other comparisons. Unfortunately, the lack of precise microenviron- 
mental information for many areas prevents detailed analysis of the possible 
correlation between other environmental factors and morphology. 
Band lengths (Table 2) and band numbers (Fig. 3) have an inverse re- 
lationship. As the average band length increases, the number of bands de- 
creases, and the snakes have a greater dark to light ratio. This is found in 
samples E, F, and G and is exemplified also by their darker head pattern. The 
Balsas-Tepalcatepec Basin is characterized by both high mean annual tempera- 
tures and high mean annual rainfall (Vivo Escoto, 1964). This suggests that a 
detailed analysis might show a correlation between mean annual temperature, 
rainfall, and/or light intensity and the number of dorsal bands and head 
pattern. Details of vegetation type and density would also have to be considered. 
Variation in band numbers among the samples may be the result of 
splitting or fusion of some of the cross bands. For example, there is an average 
increase of five body bands from population A to B, but a decrease of about 
15 scale lengths (difference between totals of six band lengths in Table 2). 
Although the light centers of many bands suggest splitting or fusion, there is no 
consistent location or number of bands which have light centers within any 
population. In addition, we were unable to derive the various band patterns 
from one another. It seems unlikely, therefore, that the light centers charac- 
teristic of many cross bands are indicative of fusion or division, a possible 
means of decreasing or increasing the band number. Differences in cross band 
numbers and lengths may represent adaptive responses to different selective 
pressures that increase or decrease the overall ratios between dark and light 
areas on the snakes. 
SYSTEMATIC TREATMENT 
Our data indicate overall similarities among the seven samples and the 
type specimens in nearly all characteristics examined. The analyses reveal 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 29 
a geographic trend towards a southern reduction in ventral-subcaudal scales 
among samples A, B, C and D and among samples E, F and G, and also point 
to the similarities among samples A, B, C and D and samples E, F and G in 
number of body bands and head pattern. Specimens with characteristics that 
are intermediate between these two groups indicate that only a single species 
is involved. Therefore, we refer our seven samples, their intermediates, and 
the types of Trimorphodon tau, upsilon, collaris, latifascia, fasciolata and 
forbesi to one species. After careful consideration and consultation, we con- 
clude that Gunther's (1895) use of Trimorphodon upsilon did not constitute 
the action of the first revisor as defined in Article 24, International Code of 
Zoological Nomenclature. Therefore, the name Trimorphodon tau is applicable 
because of the action of Smith and Darling (1952) who gave priority to tau 
rather than upsilon, by their action as first revisor. 
TRIMORPHODON TA U COPE 
Trimorphodon tau Cope, 1869, Proc. Amer. Phil. Soc, 11, p. 152 (type 
description; type locality "western part of the Isthmus of Tehuantepec, Mex- 
ico," in error); 1875, J. Acad. Natur. Sci. Philadelphia, ser. 2, 8, p. 131. Sumi- 
chrast, 1892, La Naturaleza, 6(2), p. 44 (type from Quiotepec, between Tehu- 
acan and Oaxaca). Cope, 1886, Proc. Amer. Phil. Soc, 23, p. 286; 1887, Bull. 
U.S. Natl. Mus., 32 p. 68; 1892, Proc. U.S. Natl. Mus., 14~ p. 678. Gunther, 
1895, Biologia Centrali-Americana, Reptilia, p. 174. Boulenger, 1896, Cata- 
logue of the snakes in the British Museum, vol. 3, p. 56. Mocquard, 1899, Bull. 
Soc. Phil., ser. 9, 1, p. 157. Cope, 1900, Rep. U.S. Natl. Mus. for 1898, p. 1101. 
Gadow, 1905, Proc. Zool. Soc. London, 1905, p. 224. Mocquard, 1908, in 
Dumeril and Bocourt, Mission Scientifique au Mexique et dans l'Amerique 
Centrale, 3, pp. 908, 912. do Amaral, 1929, Mem. Inst. Butantan, 4, p. 202. 
Taylor, 1939, Univ. Kansas, Sci. Bull., 25, pp. 366-67; 1940, Univ. Kansas Sci. 
Bull., 26, pp. 474-77, fig. 8, plate 51. Smith, 1941, Proc. U.S. Natl. Mus., 91, 
pp. 166-67; 1943, Proc. U.S. Natl. Mus., 93, p. 494. Smith and Taylor, 1945, 
Bull. U.S. Natl. Mus., 187, p. 148. Taylor, 1949, Univ. Kansas Sci. Bull., 33, 
pp. 210-11. Davis and Dixon, 1957, Southwestern Natur., 2, p. 24. Martin, 
1958, Misc. Publ. Mus. Zool. Univ. Michigan, 101, p. 74. Duellman, 1961, 
Univ. Kansas Publ. Mus. Nat. Hist., 15, p. 112; 1965, Univ. Kansas Publ. Mus. 
Nat. Hist., 15, pp. 655, 657, 660-61, 666, 685. Lynch and Smith, 1965, Herpe- 
tologica, 21, p. 168. Brown and Brown, 1967, Texas J. Sci., 29, p. 325. 
Eteirodipsas biscutata (in part), Jan, 1863, Elenco sistematico degli 
ofidi. . ., p. 105. Jan and Sordelli, 1872, Iconographic generale des ophidiens, 
vol. 3, livr. 39, plate 1, fig. 3. Cope, 1892, Proc. U.S. Natl. Mus., 14, p. 679 
(footnote). Gunther, 1895, Biologia Centrali-Americana, Reptilia, p. 175. 
Trimorphodon upsilon Cope, 1869, Proc. Amer. Phil. Soc, 11, p. 152 
(type description; type locality "Guadalaxara, West Mexico"); 1875, J. Acad. 
30 CONTRIBUTIONS IN SCIENCE NO. 179 
Natur. Sci. Philadelphia, ser. 2, 8, p. 131; 1886, Proc. Amer. Phil. Soc, 23, 
p. 286; 1887, Bull. U.S. Natl. Mus., 32, p. 68; 1892, Proc. U.S. Natl. Mus., 14, 
p. 678. Gunther, 1895, Biologia Centrali-Americana, Reptilia, pp. 174-75. 
Boulenger, 1896, Catalogue of the snakes in the British Museum, vol. 3, p. 55. 
Mocquard, 1899, Bull. Soc. Phil., ser. 9, 1, p. 157. Cope, 1900, Rep. U.S. Natl. 
Mus. for 1898, pp. 1104-1105, fig. 315. Gadow, 1905, Proc. Zool. Soc. London, 
1905, pp. 196, 231, 233; 1910, Zool. Jahrbuch, 29, pp. 697, 701. Mocquard, 
1908, in Dumeril and Bocourt, Mission Scientifique an Mexique et dans 
l'Amerique Centrale, 3, pp. 908, 910-11. do Amaral, 1929, Mem. Inst. Butan- 
tan, 4, p. 202. Taylor, 1939, Univ. Kansas Sci. Bull., 25, pp. 365-66, plate 35, 
fig. 2. Smith, 1941, Proc. U.S. Natl. Mus., 91, pp. 162-163; 1943, Proc. U.S. 
Natl. Mus., 93, p. 494. Smith and Taylor, 1945, Bull. U.S. Natl. Mus., 187, 
p. 148. Zweifel and Norris, 1955, Amer. Midland Natur., 54, p. 245. Duellman, 
1961, Univ. Kansas Publ. Mus. Nat. Hist., 15, p. 112. 
Dipsas biscutatus var. latifascia Peters, 1869, Monatsber. Akad. Wiss. 
Berlin, p. 877 (type description; type locality, Puebla, Mexico). 
Trimorphodon collaris Cope, 1875, J. Acad. Natur. Sci. Philadelphia, ser. 
2, 8, p. 131 (type description; type locality "Orizaba, Vera Cruz"). Sumichrast, 
1882, La Naturaleza 6(2), p. 44 (type(s) came from Tuxpango, near Ori- 
zaba); Cope, 1886, Proc. Amer. Phil. Soc, 23, p. 286; 1887, Bull. U.S. Natl. 
Mus., 32, p. 68; 1892, Proc. U.S. Natl. Mus., 14, p. 679. Gunther, 1895, 
Biologia Centrali-Americana, Reptilia, p. 174. Cope, 1900, Rep. U.S. Natl. 
Mus. for 1898, p. 1101. Taylor, 1939, Univ. Kansas Sci. Bull., 25, pp. 364-65. 
Smith, 1941, Proc. U.S. Natl. Mus., 91, pp. 165-66; 1943, Proc. U.S. Natl. 
Mus., 93, p. 493. Smith and Taylor, 1945, Bull. U.S. Natl. Mus., 187, p. 147. 
Sibon biscutatus, Garman, 1883, Mem. Mus. Comp. Zool. Harvard Univ., 
8, pp. 16, 134 (part). 
Sibon biscutatum var. latifasciatum, Garman, 1883, Mem. Mus. Comp. 
Zool. Harvard Univ., 8, pp. 16-17, 134. 
Sibon upsilon, Garman, 1883, Mem. Mus. Comp. Zool. Harvard Univ., 
8, p. 134. 
Trimorphodon biscutatus, Gunther, 1895, Biologia Centrali-Americana, 
Reptila, p. 174 (part). 
Trimorphodon upsilon var. collaris, Mocquard, 1908, in Dumeril and 
Bocourt, Mission Scientifique au Mexique et dans l'Amerique Centrale, 3 
plate 74, fig. 2, a, b. 
Trimorphodon latifascia, Taylor, 1939, Univ. Kansas Sci. Bull. 25, pp 
364-65, plate 36, fig. 2; 1940, Univ. Kansas Sci. Bull., 26, p. 479, plate 52 
Smith, 1941, Proc. U.S. Natl. Mus., 91, p. 160. Smith and Taylor, 1945, Bull 
U.S. Natl. Mus., 187, p. 148. Schmidt and Shannon, 1947, Fieldiana Zool. Chi- 
cago Nat. Hist. Mus., 31, p. 83. Hall, 1951, Univ. Kansas Sci. Bull., 34, pp 
207-08. Davis and Smith, 1953, Herpetologica, 8, p. 140. Peters, 1954, Occ 
Papers Mus. Zool. Univ. Michigan, 554, p. 32. Davis and Dixon, 1957, South 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 31 
western Natur., 2, p. 23. Webb and Fugler, 1957, Herpetologica, 13, p. 33. 
Duellman, 1958, Occ. Papers Mus. Zool. Univ. Michigan 589, p. 12. Davis 
and Dixon, 1959, Proc. Biol. Soc. Washington, 72, p. 88. Duellman, 1961, 
Univ. Kansas Publ. Mus. Natur. Hist., 15, pp. 111-12. Fouquette and Ross- 
man, 1963, Herpetologica, 19, p. 199. Duellman, 1965, Univ. Kansas Publ. 
Mus. Nat. Hist., 15, pp. 655-56, 659, 680, 699. 
Trimorphodon fasciolata Smith, 1941, Proc. U.S. Natl. Mus., (type de- 
scription; type locality "near Zararacua [sic] Falls, 6 kilometers southeast of 
Uruapan, Michoacan.") 91, pp. 160-62; 1943, Proc. U.S. Natl. Mus., 93, p. 
493. Smith and Taylor, 1945, Bull. U.S. Natl. Mus., 187, p. 147. Schmidt and 
Shannon, 1947, Fieldiana Zool. Chicago Nat. Hist. Mus., 31, p. 83. Davis and 
Smith, 1953, Herpetologica, 8, p. 140. Peters, 1954. Occ. Papers Mus. Zool. 
Univ. Michigan, 554, pp. 32-34. Davis and Dixon, 1957, Southwestern Natur. 
2, p. 23. 
Trimorphodon forbesi Smith, 1941, Proc. U.S. Natl. Mus., 91, pp. 163-65 
(type description; type locality "from San Diego [about 5 miles south of 
Tehuacan], Puebla"); 1943, Proc. U.S. Natl. Mus., 93, p. 493. Smith and 
Taylor, 1945, Bull. U.S. Natl. Mus., 187, p. 147. 
Trimorphodon tau tau, Smith and Darling, 1952, Herpetologica, 8, p. 85. 
Trimorphodon tau upsilon, Smith and Darling, 1952, Herpetologica, 8, 
p. 85. Zweifel, 1959, Amer. Mus. Novitates, 1949, pp. 3-4, 6-8. 
Description.?A species of Trimorphodon with 201-231 ventral and 61- 
85 subcaudal scales in males; 210-243 ventrals and 55-80 subcaudals in fe- 
males; 265-319 total ventral-subcaudal scales; a divided anal scale; usually 3 
(2-5) loreal scales, 3 (1-4) preocular, 3 (2-4) postocular, 3 (1-5) primary 
temporal, 4 (2-5) secondary temporal, 8 (7-10) supralabial with the fourth 
and fifth (third-sixth) bordering the eye, and 12 (9-14) infralabial scales 
usually separated from the chin shields at the sixth (fourth-seventh) infra- 
labial; dorsal scales usually in 22, 23, or 24 (21-27) rows at one head length 
behind the head, 22 or 23 (17-25) rows at midbody, and 15 or 16 (14-18) rows 
at one head length in front of the anus. 
The snakes are usually gray, tan or light brown in ground color and 
crossed by 18-46 body bands that usually reach the edges of the ventral and 
subcaudal scales. The cross bands are various shades of brown or black and 
often darkest along their margins. Most dark cross bands have lighter central 
areas that approach the ground color. These central areas may be large and 
diffuse or concentrated into discrete spots. They suggest the splitting of one 
band or fusion of two bands. The cross bands decrease in length on the midline 
from anterior to posterior. Often the first cross band is considerably larger 
than the second. The cross bands are widest dorsally and taper to a broad or 
narrow base laterally. Laterally, small, irregular interband spots may be 
present. Frequently the body bands continue onto the abdominal scales giving 
32 CONTRIBUTIONS IN SCIENCE NO. 179 
the ventral surface an irregular blotched pattern. However, in some specimens 
the abdominal scales are irregularly spotted or nearly immaculate. 
The head pattern is extremely variable (see discussion). It consists of a 
dark head cap extending from the snout to the posterior parts of the parietals 
where it usually is separated from the first cross band by a light nuchal collar. 
In some specimens the snout is light. There may be a prefrontal bar, an inter- 
ocular bar, a parietal mark and an occipital spot or any combination of these 
components. In some specimens most or all of the head cap components may 
be lacking, and the head is uniformly dark brown. 
The nuchal collar sometimes extends medially onto the parietal area to 
connect with the parietal mark. In this instance the anterior border of the 
collar is chevron-shaped. Often the nuchal collar is straight or slightly indented 
anteromedially. The posterior border of the collar is nearly always straight. The 
first body blotch occasionally contacts the head cap or may be separated from 
it one-half to six dorsal scales. The collar is usually three scales long on the 
midline. 
Subspecies.?The numbers of cross bands, the cross band lengths, and the 
head pattern indicate that gene flow between samples B and G is limited. The 
geographic barrier of the Transverse Volcanic Range separating these two 
samples may be partly or wholly responsible for this apparent restriction of 
gene flow. Presumably these two populations have come into secondary con- 
tact after experiencing separate histories. In our opinion, these two samples 
do not represent a continuum that was split into two components by the uplift 
of the Transverse Volcanic Range. It seems more likely that population G 
evolved from ancestors that moved into the Tepalcatepec Basin from the 
south after the Transverse Volcanic Range reached its present height in Jalisco 
and Michoacan (see discussion below). The similarities between the Balsas- 
Tepalcatepec samples E, F and G and their differences from A, B, C and D 
support this view. The latter four samples are similar in several characteristics 
and probably are representative of a continuum, as indicated by specimens 
from intermediate localities. There appears to have been some genetic exchange 
between the two groups through samples F and D in some of the river valleys 
of southeastern Puebla, northeastern Oaxaca and eastern Veracruz. 
The similarities and differences between A B, C and D and between E, F 
and G have been thoroughly discussed. Consideration of these points, com- 
bined with the apparent geographic barriers between these two groups, at this 
time leads us to recognize them as subspecies. The specimens representative of 
samples A, B, C and D and their intermediates are referred to Trimorphodon 
tau tau. The specimens from samples E, F and G in the Balsas-Tepalcatepec 
Basin are referred to Trimorphodon tau latifascia (new combination). 
Distribution and ecology.?Trimorphodon tau is widely distributed along 
the coastal slopes and foothills of the Sierra Madre Occidental and Sierra 
Madre Oriental (Fig. 1). Occasaional specimens have been taken on the coastal 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 33 
plains. The species is found in suitable habitats to the north of the Transverse 
Volcanic Range and the high southern portions of the Mexican Plateau. 
Trimorphodon tau has also been recorded from scattered localities to the east 
and south of the Mexican Plateau, from the Valley of Oaxaca south and east of 
the Sierra Madre del Sur. The species is widely distributed in the foothills of 
the Balsas and Tepalcatepec Basins. Although the species is reported from 
localities ranging from 100 to 2600 meters in elevation, most of the range of 
the species lies between 1000 and 2100 meters. 
The lack of adequate material from localities between samples A and B, 
between samples D and E, and between samples E and G probably reflects the 
inaccessibility of these areas as well as inadequate sampling of suitable habitat. 
Only four specimens are known from the eastern versant between samples C 
and D. We suspect that local climatic factors (high annual precipitation and 
abundant cloud cover) probably restrict the distribution of Trimorphodon to 
drier, less accessible habitats in this area. 
Trimorphodon tau is a nocturnal species that occupies semi-arid to season- 
ally dry habitats. Specimens have been collected in arid tropical scrub, thorn 
woodland, tropical deciduous forest, mesquite grassland and dry pine-oak 
woodland (vegetation classifications follow Leopold, 1950). The species is 
terrestrial and commonly found in rocky areas of irregular relief. Individuals 
have been collected from beneath rocks, in holes and under bark on fence posts 
and dead trees during the day and in a flooded rice field at night. Most speci- 
mens were found on roads at night. The species feeds primarily on lizards, al- 
though frogs and small mammals probably are eaten also. Unidentifiable 
species of Sceloporus and Cnemidophorus were found in specimens from 
Guerrero, Michoacan and Oaxaca. 
Eggs and young.?Because very little is known concerning the eggs and 
young of oviparous snakes, the following data for Trimorphodon tau are ap- 
propriate. 
On July 18, 1966 a large female Trimorphodon tau (MVZ 81354) was 
collected 26 miles NW of Huajapan de Leon on Mexico Highway 190 in 
Puebla (Sample F) by J. L. LaPointe. Sometime between the date of capture 
and July 25, this snake deposited seven eggs. The eggs were incubated follow- 
ing the technique outlined by Zweifel (1961: 112-113). On September 25, one 
of the eggs was opened and found to be developing. On October 10, the eggs 
averaged 26.1 mm in length, 16.8 mm in width and 4.0 gm in weight. Five of 
the remaining six eggs hatched between October 29 and November 1, at least 
96 days after laying. The hatchlings made from 2-7 (x = 5.4) longitudinal 
slits in the egg shell to escape. The sixth egg did not hatch and was found, on 
November 4, to contain a well developed, but dead, female (MVZ 81361). 
Pertinent information for the mother and five hatchlings are presented in 
Table 3. 
The hatchling snakes are typical of sample F in the characteristics studied. 
34 CONTRIBUTIONS IN SCIENCE NO. 179 
TABLE 3. 
Data for Adult Female and Five Offspring of 
Trimorphodon tau from Puebla, Mexico 
Specimen No. (MVZ): 81354 81359 81360 81356 81357 81358 
Sex Ad. ? ? 9             $ $ S 
Weight-ems.   2.73 2.95 2.39 2.86 2.86 
SlLgth-mm. 752 199 207 199 213 219 
Snout-vent length - mm. 633 168 176 165 174 179 
tail length 15.8 15.6 14.3 17.1 18.3 18.3 
%
 total length 
Ventrals 217 218 216 195 205 203 
Subcaudals 69 67 68            80 84 78 
Ventrals & Subcaudals 217 218 216          195 205 203 
Umbilical Scar *   186 182          170 174 177 
Body Bands 28 24 ?              22 22 24 
Supralabials 8-9 8-8 9-9           8-8 9-8 8-8 
Infralabials 13-13 13-12 13-13 11-11 13-12 12-12 
* First ventral scale with scar 
Five hatchlings have 275-289 (x = 282.8) total ventral-subcaudal scales. These 
counts are very similar to counts from other Puebla specimens from the same 
general area (275-290, x = 284.75, N = 8). The same similarities exist in 
comparing the total body band counts. Four hatchlings have 22-24 (x = 23.0) 
dorsal cross bands while other Puebla specimens have 19-26 (x = 22.3, N = 9) 
cross bands. The hatchlings also agree with other Puebla specimens of Tri- 
morphodon in their supralabial and infralabial counts (Table 2). 
EVOLUTIONARY HISTORY 
Some brief comments concerning speciation in the genus Trimorphodon 
seem appropriate. Because no fossil remains are known, our interpretation of 
the evolutionary history of the species is based primarily on an analysis of the 
distributions and relationships of living forms correlated with the geohistory 
and paleogeography of the area. 
Savage (1966) considered snakes of the genus Trimorphodon to be rep- 
resentative of the Middle American Element. Duellman (1958, 1966) sug- 
gested that Trimorphodon diverged early from the evolutionary stock that gave 
rise to Hypsiglena, Leptodeira, Eridiphas and Cryophis. We concur, and sug- 
gest that the ancestor of Trimorphodon diverged early in the Cenozoic and 
probably occupied areas of relatively low relief in northern and central Mexico. 
Axelrod (1958) has indicated that most of this region was dominated by a 
Neotropical Tertiary Geoflora. Based on indirect evidence several authors have 
suggested that a broad ecotone of Arcto-Tertiary Geoflora extended into the 
mountains of Mexico at this time (Axelrod, 1960; Brame and Wake 1963; 
Savage, 1966). 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 35 
As a result of the general cooling trend in the early Tertiary, the northern 
borders of the tropics began to move towards the equator. In areas of north- 
western Mexico and the southwestern United States, elements of a Madro- 
Tertiary Geoflora, that developed in situ, began to spread. The Miocene was a 
period of major mountain building and general uplift (Maldonado-Koerdell, 
1964). The Mexican Plateau, the Sierra Madre Occidental, the Sierra Madre 
Oriental, and the Sierra Madre del Sur were uplifted to their present height 
beginning in the Miocene and continuing to the present. This period of orogeny 
initiated major volcanic action, especially during the Pliocene and Recent, that 
formed the Transverse Volcanic Range. By the end of Miocene, in response to 
the gradual Tertiary temperature depression and increasing aridity, much of 
the tropical vegetation, except the more xeric type, was eliminated from cen- 
tral and western Mexico. In northern Mexico the derivatives of the Madro- 
Tertiary Geoflora were segregating into their component parts in the late 
Cenozoic. The mixed coniferous and deciduous derivatives of the Arco- 
Tertiary Geoflora were found throughout most of the mountainous areas of 
Mexico. 
We suggest that the ancestral Trimorphodon stock gave rise to three 
distinct lineages, each of which was markedly affected by the continuing 
trends of cooling and aridity and by the late Tertiary period of mountain 
building and volcanic activity. 
The first lineage probably occupied much of central Mexico and gave 
rise to Trimorphodon tau. As the climatic changes continued, this species 
adapted to dry habitats throughout much of the present Mexican Plateau per- 
haps as far south as Oaxaca. Tamayo and West (1964) suggested that much 
of this area, originally drained by the Lerma River included the lake basins 
drained by the present Rio Lerma as far southeast as the Valley of Mexico. 
With the late Tertiary volcanic activity that gave rise to the Mesa Central 
(West, 1964) and the Transverse Volcanic Range and the resultant cooler 
temperatures, this ancestral species was eliminated from the central part of its 
range and restricted to a horseshoe pattern of distribution north, east and south 
of the Mesa Central. One segment of this population gave rise to the subspecies 
latifascia in the eastern Balsas Basin. Subsequently, when conditions were 
suitable, the Balsas population apparently expanded into the Tepalcatepec 
drainage system and approached the range of the northern segment of the 
original population. These two ends of the horseshoe are now separated by the 
western portions of the Transverse Volcanic Range. At the same time that the 
Balsas-Tepalcatepec populations were expanding, the population ancestral to 
the subspecies tau was expanding northward along the slopes and foothills of 
the Sierra Madre Occidental and Sierra Madre Oriental. 
The second major lineage of Trimorphodon evolved in association with 
the developing Madro-Tertiary Geofloral derivatives and gave rise to the 
species found in the arid lowlands of the southwestern United States and north- 
36 CONTRIBUTIONS IN SCIENCE NO. 179 
western Mexico today. We suspect that Trimorphodon vandenburghi, T. 
lambda and T. lyrophanes, if indeed they are distinct species, were derived from 
this second major lineage. Trimorphodon vilkinsonii, today found in eastern 
New Mexico, western Texas and adjacent parts of Mexico, likely was derived 
from the ancestral lyrophanes stock and isolated east of the Rocky Mountain- 
Sierra Madre Occidental mountain system, where it is found today in moun- 
tains and foothills on the margin of the Chihuahuan Desert. 
The third lineage gave rise to the species T. biscutatus and probably 
evolved in a xeric tropical lowland environment in the Pacific coastal lowlands 
of southern Mexico and northern Central America. Savage (1966) referred to 
this species in his discussion of the history of the Western Mesoamerican 
Complex. Trimorphodon biscutatus subsequently dispersed northward along 
the developing Pacific lowland route as far north as southern Jalisco. 
Areas of sympatry or near sympatry between Trimorphodon biscutatus 
and T. lambda occur in the southwestern corner of Jalisco. Trimorphodon tau 
is sympatric with Trimorphodon biscutatus at Apatzingan, Michoacan and 
Huajintlan, Morelos and with Trimorphodon lambda at Terreros, Sinaloa and 
about 10 miles west of Alamos, Sonora. Although T. tau has been reported 
from Chihuahua, Chihuahua (Cope 1900) near the type locality of Trimor- 
phodon vilkinsonii, this record needs to be verified. 
ACKNOWLEDGMENTS 
We would like to thank the following people and institutions for allowing 
us to examine material in their care: Charles M. Bogert and Richard G. Zwei- 
fel, American Museum of Natural History, New York (AMNH); Edmond V. 
Malnate and James E. Bohlke, Academy of Natural Sciences, Philadelphia 
(ANSP); M. J. Fouquette, Arizona State University, Tempe (ASU); Alice 
G. C. Grandison, British Museum (Natural History), London (BM); Richard 
B. Loomis, California State College, Long Beach (CSCLB); Robert F. Inger 
and Hymen Marx, Field Museum of Natural History, Chicago (FMNH); 
William E. Duellman, Museum of Natural History, University of Kansas, 
Lawrence (KU); John W. Wright, Los Angeles County Museum of Natural 
History, Los Angeles (LACM); Douglas A. Rossman, Louisiana State Uni- 
versity, Museum of Zoology (LSUMZ); Ernest E. Williams, Museum of 
Comparative Zoology, Harvard University, Cambridge (MCZ); Walter W. 
Dalquest, Midwestern University, Wichita Falls, Texas (MU); Robert C. 
Stebbins, Museum of Vertebrate Zoology, University of California, Berkeley 
(MVZ); George S. Myers, Museum of Natural History, Stanford University, 
Palo Alto (SU?collections now housed at California Academy of Sciences, 
San Francisco); James R. Dixon, Texas Cooperative Wildlife Collection, 
Texas A & M University, College Station (TCWC); Charles H. Lowe, Uni- 
versity of Arizona, Tucson (UAZ); Walter Auffenberg, Florida State Museum, 
University of Florida, Gainesville  (UF); Hobart M. Smith, University of 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 37 
Illinois Museum of Natural History, Urbana (UIMNH); Charles F. Walker, 
University of Michigan Museum of Zoology, Ann Arbor (UMMZ); James A. 
Peters, United States National Museum, Washington, D.C. (USNM); and 
Giinther Peters, Zoologisches Museum Humboldt-Universitat, Berlin (ZMB). 
Robert L. Bezy and C. Jay Cole, and Richard D. Worthington also provided 
specimens for study. The information on eggs and hatchlings was made avail- 
able by Joseph L. LaPointe, Ray B. Huey and Ted Papenfuss. 
Evie Templeton illustrated the head patterns in Figures 5, 6, and 7. 
Mercedes McDiarmid and Richard D. Worthington provided technical assist- 
ance with the statistical analysis. Allene J. Brown typed the manuscript. David 
B. Wake and Hymen Marx read the manuscript in final form and made several 
helpful suggestions. Fred F. Gehlbach kindly relinquished his interest in this 
group of Trimorphodon. Carl L. Hubbs, W. I. Follett and Lillian Dempster 
offered their advice concerning the proper use of the name Trimorphodon tau. 
The Society of Sigma Xi provided financial assistance to the first author 
for field work in Sinaloa in 1962. 
To all of these people and institutions we extend our thanks. 
SPECIMENS EXAMINED 
MEXICO 
Aquascalintes: 7 mi S Rincon de Romos (UIMNH 27566). 
Colima: Colima (AMNH 12777); 4.3 mi SW Colima, 575' (UMMZ 114479). 
Durango: Ventanas (BM 83.4.16.68 and 69). 
Guanajuato: Guanajuato (SU 4412, USNM 11370), Mt. Cubilete (AMNH 93433). 
Guerrero: 15 mi NE Acapulco (LACM 7114); Acahuizotla (TCWC 22142); 3 mi 
WSW Axixintla (UMMZ 126541); Chilpancingo (FMNH 38412-32; KU 24100-03; 
MCZ 33657-58, 33663-5; UIMNH 34991-93); near Chilpancingo (UMMZ 85769- 
74); vicinity of Chilpancingo (AMNH 72522-24); 4 mi W Chilpancingo, 5800' 
(TCWC 9575); 13 m S Chilpancingo, 3750' (KU 67733); 7 mi E Chilpancingo 
(UIMNH 19139); 40 mi N Chilpancingo (LACM 53026); 25 mi NNE Iguala, 
3800' (TCWC 12608); Ojito de Agua, 2.5 mi S Almolonga, 5600' (TCWC 11602- 
03); Ojito de Agua, 3 mi S Almolonga, 5400' (TCWC 11601); Omilteme, Sierra de 
Burro Mtns. (MCZ 42677); Palo Blanco, 4800' (TCWC 9574); 15 mi SE Tonatico 
(UMMZ 126542); Taxco (MCZ 33901). 
Hidalgo: 10 km N Jacala (USNM 110401); Zacualtipan (ANSP 14770); 5.6 mi N 
of road to Zimapan on Hwy 85 (LACM 53023); 5 mi S Zimapan (AMNH 93432). 
Jalisco: 2 mi ENE Acatlan, 5300' (KU 67735); 4 mi S Autlan (KU 27191); 2 mi E 
Bolaiios, 3500' (KU 91428); 1 mi NE Contla, 3800' (KU 80762-63); La Cumbre de 
los Arrastrados, 8500' [Talpa Mascota] (BM 92.10.31.63); Guadalajara (MCZ 
46891; USNM 31358-type of upsilon); between Hostotipaquillo and Magdalena 
(AMNH 19582); 10.4 km NNW Ixtlahuacan del Rio (KU 102986); Jamay (AMNH 
38 CONTRIBUTIONS IN SCIENCE NO. 179 
19841); near Magdalena, 1300 m (FMNH 105194); 1 mi NW El Molino, 5100' 
(AMNH 96652). 
Mexico: Ixtapan de la Sal, 5250' (AMNH 71360). 
Miahoacan: Apatzingan, 1000' (FMNH 39078-79); 7.6 mi E Apatzingan, 1600' 
(UMMZ 112514); 14 mi E Apatzingan, 1700' (UMMZ 112516); 17.6 mi E Apat- 
zingan, 1600' (UMMZ 112515); 3.9 mi S Apatzingan (U1MNH 73730); Coal- 
coman, 945 m (UMMZ 104696-97); 6 mi E Emiliano Zapata, 5350' (UMMZ 
118950); 7 mi E Emiliano Zapata, 5400' (UMMZ 118949); 4.3 mi N Lombardia, 
2850' (UMMZ 118951); 8.7 mi S Lombardia (UMMZ 124039); Nueva Italia, 1250' 
(UMMZ 118952); 43 mi S Nueva Italia on Playa Azul Road, 1000' (UAZ 27060); 
Tacicuaro, 2000 m (FMNH 105193; UIMNH 19138); 5.5 m W Tangamandapio, 
5800' (UMMZ 118948); 1.4 mi N Rio Tepalcatepec (UIMNH 73729); Tzararacua 
Falls, 6 km SE Uruapan (USNM 110400-type of fasciolata). 
Morelos: Alpuyeca, 3500' (TCWC 4127); 4 mi S Alpuyeca, 3600' (UMMZ 114478); 
Campo Agricola, Progreso (UIMNH 26073); camp near Cuernavaca (UIMNH 
19135); Huajintlan (UIMNH 19137); km 128, near Puente de Ixtla (FMNH 
105100); 12 mi S Puente de Ixtla (UIMNH 19134); Tepoztlan (UIMNH 19136); 
6 mi W Yautepec (TCWC 7390). 
Nayarit: Barranquitas (AMNH 75585); 5 mi SE Ixtlan del Rio (TCWC 12609); N 
of San Bias (LACM 53025). 
Oaxaca: Juquila Mixes [=Xuquila Mixes] (AMNH 100649); 3 mi NE Mitla, 5800' 
(AMNH 97985); ca. 2 mi W Mitla, La Fortaleza (AMNH 89629); 17 mi SE 
Nochixtlan, 6900' (TCWC 12640); Oaxaca (FMNH 105305, 105350); 21 mi SE 
Oaxaca, 5350' (UMMZ 112522); 59 mi NW Ciudad Oaxaca, (UMMZ 121824); 
Quiotepec (USNM 30338-type of tau); San Felipe del Agua, 6500' (AMNH 97988, 
100932-33); 2 km W San Felipe del Agua, (UIMNH 60799); Cerro San Felipe 
(UIMNH 53121, 73654, 74462-64); San Lucas Camotlan (AMNH 89630); 3 mi N 
San Miguel del Valle, 6950' (AMNH 97986-87). 
Puebla: no specific locality (ZMB 6652-syntypes of latifascia); 11.4 mi NW Acatlan 
(LACM 38206); 16 mi N Acatlan (LACM 9509); 6 mi SE Acatlan (KU 31680); 
10.1 mi NW Amatitlan (UF 11337); 10 mi NW Huajuapan de Leon on Hwy 190 
(MVZ 81355); 26 mi NW Huajuapan de Leon on Hwy 190 (MVZ 81354); 3 km W 
Izucar de Matamoros (KU 39625); 17 mi SE Iziicar de Matamoros (AMNH 
89631); San Diego, ca. 5 mi S Tehuacan (USNM 110402-type of forbesi); 6.7 mi 
NNW Tehuitzingo (UF 11335); 6.3 mi SE Tehuitzingo (UF 11336). 
San Luis Potosi: 10.5 mi W Rioverde, 4000' (UMMZ 126193); 2.5 mi S Pendencia 
(LSUMZ298). 
Sinaloa: 16 km NNE Choix, 1700' (KU 68754); 22.1 mi N Culiacan (LACM 
53024); 4 mi NNE El Fuerte, 300' (FMNH 71531) 2-3 mi ESE Rio Fuerte Dam 
[8 mi NNE El Fuerte, 300'] (FMNH 71532-33) 8.3 mi N Guacamil [=Gua- 
muchil] (UF 12829); 1.6 mi S Guacamil [=Guamuchil] (UF 12830); Terreros 
(LACM 9510); near Terreros (LACM 7112); 2.5 mi NW Terreros (LACM 7108); 
5 mi NW Terreros (LACM 7109); 7 mi NW Terreros (LACM 7111); 10 mi NW 
Terreros (LACM 7110); 10.2 mi SE Terreros (LACM 7113). 
Sonora: La Aduana, 5 mi W Alamos (LACM 53028); Alamos (AMNH 75119); W 
1970 GEOGRAPHIC VARIATION OF MEXICAN LYRE SNAKES 39 
side Alamos (KU 24119); 3.5 mi W Alamos (LACM 9157); 9.7 mi W Alamos, 
1300' (LACM 53029); 8 mi SSE Alamos on Rio Cuchujaqui, 900' (LACM 53030); 
Guirocoba (MVZ 50833-34); ca.  15 mi SE Navojoa (MVZ 76372);  18 mi SE 
Navojoa (MVZ 76373); 20 mi E Navojoa (LACM 53027). 
Tamaulipas: 10 km N Antiguo Morelos (MU 196); S Ciudad Victoria, on Hwy 85 
betweenC. Victoria and Llera (UMMZ 111255); 13 mi S Ciudad Victoria (UIMNH 
19284); 14 mi S Ciudad Victoria (UIMNH 27164); 23 mi S Ciudad Victoria 
(AMNH 72399); 24 mi S Ciudad Victoria (AMNH 72400); Gruta de Quintero, near 
Quintero (AMNH 58224); La Joya de Salas, 1550 m (UMMZ 110882). 
VeraCruz: Jalapa (BM 81.10.31.65); Tuxpango, near Orizaba (USNM 26499-type 
of collar is). 
Zacatecas: Hacienda San Juan Capistrano (USNM 46334). 
Locality Unknown:  "Mexico" (FMNH 42066; USNM 9911-12, 25361, 26138-9 
[see Taylor, 1939: 366 for comments]). 
"Southern Mexico" (BM 95.1.4.7 A and B) 
"Districto Federal" (AMNH 19718 [see Zweifel, 1959: 7 for comments]). 
ADDITIONAL SPECIMENS {examined but data not included) 
Colima: 4.3 mi SSW Colima, 1300' (UF 24783). 
Hidalgo: 10.4 mi NNW Ixmiquilpan, 7500' (UF 27378). 
Jalisco: 2 mi NE El Molino (UAZ 27023). 
Sonora: 6 mi W Alamos (ASU 6651, 6684); 9 mi W Alamos (ASU6377); 11 mi W 
Alamos (ASU 6663, 6712); 14 mi W Alamos (ASU 6648). 
LITERATURE RECORDS {specimens not examined) 
Chihuahua: Batopilas (Cope, 1887: 68;Klauber, 1928: plate 22); city of Chihuahua 
(Cope, 1900: 1105). 
Jalisco: "Jalisco" (Mocquard, 1899:  157); Guadalajara [USNM 12419]  (Taylor, 
1939: 366; Smith, 1941: 163). 
Michoacan: San Salvador [BM 1914.1.28.136] (Peters, 1954: 32-34). 
Morelos: between Cuernavaca and Tepoztlan; near Huajintlan (Taylor, 1941: 479). 
Nayarit: Sierra del Nayarit (Mocquard, 1899: 157). 
Tamaulipas: 14 mi SW Jimenez (Brown and Brown, 1967: 325). 
RESUMEN 
La variation geografica en lepidosis y tipo de coloration han sido es- 
tudiadas en las siguientes especies nominales Trimorphodon collaris, fasciolata, 
forbesi, latifascia, tau y upsilon. Los ejemplares fueron agrupados en siete 
diferentes muestras geograficas que fueron luego comparadas entre si. La 
mayoria de las caracteristicas tienen una amplia distribution y se confunden 
mas con otras; otras caracteristicas varian independientemente. Las escamas 
ventrales y subcaudales disminuyen en numero de norte a sur. El numero de 
bandas dorsales en el cuerpo es menor en culebras del Valle de Balsas- 
40 CONTRIBUTIONS IN SCIENCE NO. 179 
Tepalcatepec, las cuales tienen tambien coloration uniforme en la cabeza. 
Ejemplares de otras regiones tienen una compleja coloration cefalica que 
consiste en bandas prefrontales, bandas interoculares y marcas parietales 
discretas en varias combinaciones. Estudios de los bandas en el cuerpo y 
coloration cefalica indican un intercambio genetico limitado entre los ejem- 
plares del Valle de Balsas-Tepalcatepec y aquellos de otras regiones, posi- 
blemente como resultado de contacto secundario en el sur de Jalisco y la region 
adyascente de Michoacan. La Cadena Volcanica Transversa y la Sierra Madre 
del Sur aparentemente restringen el intercambio genetico. 
Estas especies nominales se asignan al sinonimo Trimorphodon tau. El 
nombre Trimorphodon tau tau se conserva para las poblaciones de las colinas 
y la meseta y T. tau latifascia (nueva combination) se asigua a la pobla- 
cion del Valle de Balsas-Tepalcatepec. Trimorphodon tau es redescribo y se 
delimita su distribution. La variation en caracteristicas de un grupo procedente 
de Puebla es semejante a la variation tipica que se encuentra en la muestra 
total de Puebla. 
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Accepted for publication June 30, 1969. 
The editors of the Los Angeles County Museum of Natural 
History Contributions in Science regret several errors 
in the text and an error in the spacing of Table 1, on 
page 11, in Contributions in Science No. 179, by Roy W. 
McMarmid and Nonaan J. Scott, Jr. We enclose errata 
sheets. We regret these inconveniences. 
Virginia JJ. Miller, 
Editor 
Robert J. Lavenberg, 
Managing Editor 
ERRATA 
In McDiarmid, Roy W., and Norman J. Scott, Jr., Geographic variation and 
systematic status of Mexican Lyre snakes of the Trimorphodon tau group 
(Colubriae), Los Angeles Co. Mus. Nat. Hist., Contrib. in Sci., No. 179, 
February 25, 1970. 
Page 5, paragraph 3, line 1: delete comma and add parenthesis after word 
"specimens." 
Page 5, paragraph 5, line 2: change "Protosi" to "Potosi." 
Page 6, paragraph 4, line 1: change "20" to "201." 
Page 8, paragraph 3, line 3: change "although!" to "although." 
Page 10, paragraph 6, line 7: change "83.33" to "83." 
Page 13, paragraph 6, line 3: delete accent on word "band." 
Page 16, paragraph 3, line 13: change "continue" to "continues." 
Page 32, paragraph 6, line 3: change "Occasaional" to "Occasionally." 
Page 33, paragraph 5, line 9: change "x" to "x." 
Page 34, Table 3, line 6: should be 
%taiHength_   J5 g ^ U3 m Jg 3 Jg 3 
total length 
Table 3, line 9: should be 
286   285   284   275   289   281 
Page 35, paragraph 1, line 15: change "Arco-" to "Arcto-." 
Page 41, line 15: change "Dumeril" to "Dumeril." 
Page 42, line 15: delete italics on "Dumeril." 
Page 43, line 1: change "Vivo Escoto" to "Vivo Escoto."