THE WEST MffiEICAN MOLLUSKS OF THE GENUSAI^lPHITHAEA^rUS.By Paul Bartsch,Assistant Curator, Division of MoUushs, U. S. National Miiseum.The genus AmpMihalainus was established by Dr. P. P. Carpenterin 1SG5 ^ for Amyhitlialamus indusus Carpenter. Watson's nameScrobs ' is a synonym of it. In 1S66 Carpenter described anotherspecies, AmpMthalamus lacunatus Carpenter.^To these I now add a third, Ampliithal'amus tenuis, also fromCalifornia.Of these three, A. indusus Carpenter has a peripheral cord; A.tenuis Bartsch, a faint raised line only; A. indusus Carpenter isbroadly conic; A. tenuis Bartsch, elongate ovate. In A. lacunatusCarpenter there is no peripheral cord.AMPHITHALAMUS LACUNATUS Carpenter.Amphithalamus lacunatus Carpenter, Proc. California Acad. Nat. Sci., vol. 3,1866, p. 218.Shell minute, broadly conic, milk-white. Nuclear whorls one andone-half, well rounded, marked by about 15 slender,equal and equally spaced, spiral threads and nu-merous, very fine, axial threads, lending the sur-face a very minutely pitted appearance. Post-nuclear whorls feebly shouldered at the summit,slightly rounded, marked b}' incremental lines only.Suture well impressed. Periphery of the last whorlinflated, rounded. Base moderately long, slightlyrounded, with a narrow umbilical chink. Apertureincomplete (outer lip fractured) ; inner lip curved,appressed; parietal wall covered with a thick callus, fig. i.?amphithala-Doctor Carpenter's type (Cat. No. 15564, ^Z''^'^'^^'"'" '''"^'U.S.N.M.) has two post-nuclear whorls and meas-res: Length 1. 5mm., diameter 1.1 mm. It comes from shell wash-ings at San Pedro, California.
1 Ann. Mag. Nat. Hist., ser. 3., vol. 15, p. 181.2 Challenger Report, 1886, p. 611.3 Proc. California Acad. Nat. Sci., vol. 3, 18G6, p. 218.Proceedings U. S. National Museum, Vol. 41?No. 1854. 263
264 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41.AMPHITHALAMUS INCLUSUS Carpenter.AmpMthalamus indusus Carpenter, Ann. Mag. Nat. Hist., ser. 3, vol. 15, 1865,p. 181.Shell elongate-ovate, purplish brown with the nuclear whorlsyellowish white. Nuclear whorls about one and one-half, well-rounded, marked by about 15 slender, equal and equally spaced,spiral threads and numerous, very fine, axial threads, lending tliesurface a very minutely-pitted appearance. Post-nuclear whorlssubtabulatedly shouldered at the summit, well rounded on themiddle, marked by fine lines of growth only. Suture well impressed.Periphery of the last whorl marked by a rather broad, low, rounded,spiral thread, which is separated from the space posterior to it by anarrow, shallow, spiral sulcus. Anteriorly, this cord passes, withoutdemarcation, into the general surface of the moderately long andgently rounded base. Base broadly umbilicated, having a ratherbroad, low, spiral cord a little posterior to the in-sertion of the columella. Aperture oval, veryoblique, reenforced within by an iimer peristomewhich, in the anterior portion of the outer lip, fuseswith it, while the columellar portion and the pa-rietal portion stand at a considerable distance fromthe columella and the parietal wall, being connectedwith these by a concave bridge of shelly matter;columella moderately long and stout.Doctor Carpenter's cotypes, three specimens (Cat.Fig. 2.?amphithala- No. 15573, U.S.N.M.), come from San Diego, Cali-Mus INCLUSUS Car- ^ -^ rpj^^ largest of these has two and one-halfPENTER. opost-nuclear whorls, and measures: Length 1.4 mm.,diameter 0.9 mm. Cat. No. 105464, U.S.N.M., contains two speci-mens, also from San Diego, and Cat. No. 213540, U.S.N.M., containsone, from Catalina Island, California.AMPHITHALAMUS TENUIS, new species.Shell elongate-ovate, dark greenish horn-color, with the columellaand the aperture yellowish white, excepting the dark edge of theperistome. Nuclear whorls one and one-half, well rounded, markedby about 15 slender, equal and equally spaced, spiral threads andnumerous, very fine, axial threads, lending the surface a very mi-nutely-pitted appearance. Post-nuclear whorls very narrowly sub-tabulatedly shouldered at the summit, well rounded, smooth except-ing fine, incremental lines. Suture moderately impressed. Periph-ery of the last whorl well rounded. Base long, well rounded, bearinga low, broad, spiral cord on its middle, wliich bounds the posteriortermination of the white area. Aperture oval, very oblique; peris-
NO. 1854. NEW WEST AMERICAN M0LLUSK8?BART8CII. 265tome double, the inner fusing with the anterior portion of the outerhp, while posteriorly it is distinct and at a considerable distancefrom the columella and the parietal wall; the spacebetween the columella, parietal wall and the innerperistome is bridged over by a concave band of shellymatter.The type (Cat. No. 213541, U.S.N.M.) has two anda half post-nuclear whorls and measures: Length1.1 nun., diameter 0.7 mm. It and another specimen,entered under the same catalogue number, were takenfrom sea moss at La Jolla, California, by Mr. F. W.Kelsey, in whose collection there are nine additionalspecimens from the same locality. Another specimen(Cat. No. 32374, U.S.N.M.) comes from Monterey,California, while seventeen more (Cat, No. 186026, U.S.N.M.) weretaken from mossy rocks at low tide at San Diego, California.
Fig. 3.?Amphitha-lamus tenuisBartsch.