PRISODON 1 221 



next longest, and the dorsal slope the shortest. The blunt, 

 posterior point is at the base of the shell instead of being 

 elevated as in obliqnus. According to Hupe it must be more 

 ponderous than that species. 



Prisodon obliquus Schumacher. 



Shell large, elongated, irregularly sutriangular, inequilateral, 

 solid; beaks full but not greatly elevated; dorsal outline 

 straight, slightly incurved or curved upwards in the middle, 

 ending in a sharp, narrow wing in front and a blunt one behind ; 

 posterior ridge well developed, narrowly rounded, sometimes 

 semi-double below, ending in a point at some distance above 

 the base; surface rather strongly, concentrically sculptured, 

 with traces of radial sculpture ; the young shells are sometimes 

 plicate on the upper part of the dorsal slope; epidermis pale 

 to dark tawny or brownish, often tinted green, shining ; pseudo- 

 cardinals compressed, elongated, split up and ragged; laterals 

 remote; muscle scars impressed; nacre flesh-colored. 

 Length 165, height 80, diam, 43 mm. 

 Amazon drainage; southward through Brazil. 

 Prisodon obliquiis Schumacher, Ess. Nouv. Syst., 1817, p. 



139, pi. xiv, fig. 2. — Simpson, Syn., igoo, p. 871. 

 Hyria obliqua PyUTEl, Conch. Sam., Ill, 1890, p. 189. 

 Hyria aviciilaris Lamarck, An. sans Vert., VI, 1819, p. 82. — 

 Crouch, 111. Int. Lam.. 1827, p. 16, pi. ix, figs. 5a, 5&. — 

 Wyatt, Man. Conch., 1838, p. 67, pi. v, fig. 4. — DelEssert, 

 Rec. Coq. Lam., 1841, pi. xii, fig. 9. — Hani^ey, Biv. Shells,, 

 1843, P- 214, pi. XXIV, fig. 11.^ — Troschee, Arch, fur Nat., 

 XIII, Ft. I, 1847, P- 271, pi. VI, fig. 3. — Chenu, Man., 1859, 



II, p. 149, fig. 734. — SowERBY, Conch. Icon., XVII, 1869, pi. 



III, figs. 6a, b. 



Unio avicularis Deshayes. Tr. El. Conch., 1839, p. 18, pi. xxix, 



figs. 10, II. 

 Hyria azncularia GuERIN, Icon. Reg. An., 1844, II, pi. xxviii, 



fig. 8. 

 Unio cmidatus Wagner, Test. Fluv. Bras., 1827, p. 35. pi. 



xxvii, figs. I, 2. 



