A NEW GENUS AND TWO NEW SPECIES OF SOUTHAMERICAN FRESH-WATER MUSSELSBy William B. MarshallAssistant Curator, Division of Mollusks, United States National Museum
The new genus here described affords a resting place for the uniquespecies described by Higgins as Mycetopus falcatus and which, in thepast has been shifted from the genus Mycetopoda (Mycetopus) of thefamily Mutelidae to the genus Solenaia of the family Unionidae, andback to Mycetopoda.The new species of Anodoniiies and Mycetopoda were collected byDr. Henry Pittier, of Caracas, Venezuela, whose donations from timeto time have enriched the collection of the United States NationalMuseum with material collected in that country.MYCETOPODELLA, new genusShell very elongate, falcate, wide at the rear, much narrower infront where each valve has a radial swelling and abruptly descends.A marked, broad, radial constriction from the beaks to the ventralmargin. Beaks very near the anterior end. Hinge line withoutteeth, nearly straight behind the beaks, just in front of the beaks itis slightly excavated and has a decided hmule. It then abruptlymerges into the anterior margin. Ligament very long. Sinuluslong, narrow, forming a very acute triangle. Posterior ridge sharp;anterior ridge much more pronounced. Posterior area roughened bynumerous, nearly perpendicular growth hnes and slight lamellationsof periostracum. Anterior area rougher with many sharply curving,deeply impressed growth Hnes. Ventral area nearly smooth andslightly glossy, but with moderate growth lines which run horizon-tally. Periostracum dull, with numerous microscopic radiating striaelike those usually found in the Mutelidae. These lines number about90 per millimeter. Anterior adductor scar pyriform, rather deep,placed far forward. Posterior adductor scar scarcely visible. Sev-eral minor but well-marked muscle scars just behind the anterioradductor scar.The above generic name is proposed for the single species nowknown, described by Higgins as Mycetopus falcatus. This shell cannot be placed in the genus Solenaia, and in many characters it differsso widely from Mycetopoda, as shown below, that it should not beincluded in that genus.No. 2678.-PROCEEDINGS U. S. NATIONAL MUSEUM. VOL. 7I,ABT. 62894&-27 1
2 PROCEEDINGS OF THE NATIONAL. MUSEUM vol.71The history of the species is shown below:MYCETOPODELLA FALCATA (Higgins) MarshallPlate 1, fig8. 1-31868. Mycetopus falcatus Higgins, Proc. Zool. Soc, London, p. 179, pi. 14, fig. 6.1868. Mycetopus falcatus Higgins, Sowerby, Conch. Icon., vol. 16, pi. 4, fig. 9.1870. Platiris (Mycetopus) falcatus (Higgins) Lea, Synopsis, p. 90,1875. Mycetopus falcatus Higgins, Clessin, Conch. Cab., p. 204, pi. 67, fig. 12.1875. Mycetopus falcatus Higgins, Fischer, Journ. de Conch., vol. 38, p. 8.1900. Solenaia falcata (Higgins) Simpson, Synopsis Naiades, Proc. U. S. Nat. Miis.,vol. 22, p. 656.1914. Solenaia falcata (Higgins) Simpson, Descr. Cat. Naiades, vol. 1, p. 458.1916. Mycetopoda bolivari Haas, Trabajos Mus. Nacional de Ciencias Naturales,Madrid, Zool. Ser., No. 25, p. 57, fig. 2.1925. (Genus?) falcata (Higgins) Marshall, Microscopic sculpture of pearly,fresh-water mussel shells, Proc. U. S. Nat. Mus., vol. 67, pp. 10-12, pi.4, fig. 1.1926. Mycetopoda falcata (Higgins) Ihering, Nautilus, vol. 39, p. 116.This is one of the most interesting shells in the whole group ofpearly fresh-water mussels. It resembles Mycetopoda but lacks thesmooth, shining periostracum and differs in microscopic sculpture,in the falcate form and in the peculiar downward bending anteriorend. It resembles also Solenaia, especially the species emarginataLea of Siam, of which it is almost an exact miniature. The resem-blance is remarkable in that the anterior end of the shell curvesabruptly downward in both genera and gives a falcate form to theshells. They also resemble each other in color and in dullness andgeneral appearance of periostracum. They differ in habitat
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Solenaialiving in Southeastern Asia Mycetopodella in South America, so faras known at present in the upper Amazon. They differ also in thestructure of the periostracum. At present this is the most importantdifference known. The microscopic sculpture of Mycetopodella is com-posed of numerous radiating striae which prove the shell to belongin the family Mutelidae. Solenaia does not have this style of sculp-ture and this is an indication that it is not a Mutelid. This belief isfurther strengthened by the anatomy of Solenaia which shows it tobelong to the Tetragenae in the family Unionidae.Marshall ^ discusses the microscopic sculpture on the periostracumof Mycetopodella falcata and the absence of close relationship betweenthis shell and the genus Solenaia. The superficial resemblancebetween the two genera is remarkable. It is paralleled in other casesin which there is a superficial appearance of relationship or perhaps areal affinity between South American and southeastern Asiatic shells.The genus Acostaea (Mulleria) ,ior instance, is supposed to include twospecies, A. lohata Ferrussac (the type of the genus), which occurs in
> Proc. U. S. Nat. Mus., vol. 67, 192.'i, pp. 10-12.
AST. 6 NEW FRESH-WATER MUSSELS MARSHALL 6the Republic of Colombia, and A. dalyi E. A. Smith of India. Thewidely separated habitats of the two species leads one to suspect thatwhen the anatomy of Acostaea lohata becomes known it may differ inimportant respects from that of A. dalyi and cause the latter to beplaced in another genus. The anatomy of A. dalyi is known, butuntil the anatomy of A. lohata becomes known dalyi must rest in thegenus Acostaea, for wide geographic separation, while usually indica-tive of lack of close relationship, is not a taxonomic character.Another instance of resemblance between shells of these two widelyseparated regions, is in the equilaterally triangular sinulus of SouthAmerican Anodonta-like fresh-water mussels which is duplicated inAnodonta-like shells of the genus Pilsbryoconcha of Siam, Cambodia,Sumatra, and Java. They belong to different families, the former tothe Mutelidae and the latter to the Unionidae.The reason for the abrupt downward bending of the anterior end ofMycetopodella and Solenaia is unkown. Probably it has something todo with enabling the mollusk to make a firm anchorage in the bottomof streams. It calls to mind the anterior end of the genus Bartlettiaof the family Aetheriidae which is specialized for anchoring purposes.ANODONTITES GUANARENSIS, new speciesPlate 1, figs. 4-6Shell rather thin, somewhat compressed, outline nearly oval,rounded and narrower in front, bluntly pointed and subtruncate atthe rear. Dorsal line nearly straight and making an obtuse anglewith the posterior margin. Ventral line curved, slightly swollenjust behind the middle, regularly rounding into the anterior margin,which in turn rounds into the dorsal margin. The ventral anddorsal margins form a blunt point just below the middle of the pos-terior margin. Posterior ridge low and regularly rounded, but em-phasized by a broad fuscous stripe radiating from the beak; the pos-terior area with two similar but narrower fuscous rays. Anterior tothe posterior ridge the periostracum is smoothish but with indis-tinct radiating striae. Anterior half of the shell polished and witha number of radiating lines of rufflings. Posterior portion plentifullycovered with low periostracal laminae. Microscopic sculpture offine radiating striae commonly found in shells of the Mutelidae.Color ashy to brownish olive, the concentric growth lines darker;interior bluish white, highly iridescent around the margin and withiridescent radiating fine lines. Prismatic edging rather broad, pallialline about 5.6 millimeters from the margin.The type. Cat. No. 365225, U.S.N.M., measures: Length 54 mm.;height, 30 mm.; diameter, 16 mm. It and a paratype, Cat. No.365226, U.S.N.M., were presented by Dr. Henry Pittier, who collectedthem in a dried lagoon at Mata Verde, near Guanare. Portuguesa.
4 PROCEEDINGS OF THE NATIONAL MUSEUM vou 71Venezuela, December 28, 1925. This locality is in the northwesternpart of Venezuela and is drained by the River Portuguesa, which,like almost all streams in Venezuela, is a part of the Orinoco system.This species is related to several other species but seems to standin a section by itself. The slight swelling on the ventral marginindicates some relationship to the shells of the group A . trigonus Spix,while the radiating rufflings show a resemblance to those of A . tortilisLea and others of that group.MYCETOPODA PITTIERI, new speciesPlate 2Shell very elongate, nearly a parallelogram, slightly wider poste-riorly. Dorsal margin straight, rounding into the posterior margin,and forming an angle with the anterior margin. Beaks set far for-ward. Ventral margin nearly straight, passing into the posteriormargin in a rounded point and curving regularly into the anteriormargin. Posterior ridge low and rounded and posterior dorsal areawith faint indications of two radiating grooves. Anterior half of theshell smooth and polished, posterior half dull and smoothish butwith minute reticulating periostracal lamellae. Whole surface infront of the posterior ridge with faint radiating striae. Front halfyellowish to greenish olive with a very dark edging along the margin.Posterior half brownish. Interior bluish, appearing radiately striate,not very iridescent. All the adductor scars but slightly impressed.Pallial line about 9 millimeters from the margin. Prismatic borderrather broad.The type. Cat. No. 365227, U.S.N.M., measures: Length, 104.5mm.; height, 35 mm.; diameter, 20.5 mm.Dr. H. Pittier obtained the type and two paratypes (Cat. No.365228, U.S.N.M.) at the same locality as the preceding species.This species is most nearly related to Mycetopoda pygmaea Spix,from which it differs chiefly in being of much greater size. Its coloris different, it lacks the prominent radiating rufflings found on pyg-maea, its posterior ridge is not so sharply defined, and the anteriordorsal line forms a more angular junction with the anterior margin.The two paratypes are almost uniform in size, color, and other detailswith the type. EXPLANATION OF PLATESPlate 1Figs. 1, 2, 3. Mycetopodella jalcata {Yiiggins) Marshall. Type of the new genus.4, 5, 6. Anodontites guanarensis, new species. Type.Plate 2Mycetopoda pittieri, new species. Type.o
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 71. ART. 6 PLATE I
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Mycetopodella falcata and Anodontites guanarensisFor explanation of plate see page 4
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 71, ART. 6 PLATE 2
Mycetopoda pittieri, new speciesFor explanation of plate see page 4