I28o DIPI.ODON 



valve with two small pseudocardinals and two remote laterals ; 

 right valve with two pseudocardinals, the upper very small, 

 and one lateral ; muscle scars shallow ; nacre bluish-white. 



Length 44, height 32, diam. 20 mm. 



Uruguay River, South America. 

 Uuio perceformis Lea, Pr. Ac. N. Sci. Phila., IV, i860, p. 90; 



Jl. Ac. N. Sci. Phila., V , 1863, p. 384, pi. xuii, fig. 292 ; Ohs., 



X, 1863, p. 20, pi. xijii, fig. 292. — SowERBY, Conch. Icon., 



XVI, 1868, pi. i.xxxiv, fig. 443. 

 Mar gar on (Unio) percrformis Lea, Syn.. 1870, p. 55. 

 Diplodon penvfonnis Simpson, Syn., 1900, p. 886. 



Probably the type, the only shell I have seen, is a young- 

 shell. It is considerably inflated and very much produced just 

 behind the middle of the base. 



DiPLODox FONTAiNiANiJS (d'Orbiguy). 



Shell unevenly obovate or subtrapezoidal, scarcely inflated, 

 the greatest diameter being in the middle of the shell, the front 

 part being wedge-shaped, with moderately full but not high 

 beaks, which are situated in front of the center, the dorsal line 

 in front of them strongly incurved ; beak sculpture radial, 

 sometimes subnodulous ; posterior ridge full, rounded, ending 

 behind in a rounded projection near the base; dorsal line 

 curved behind the beaks, obtusely angled where it meets the 

 posterior truncation ; surface with fine, concentric growth 

 striae, often with faint traces of radial sculpture ; epidermis 

 greenish-brown to blackish, scarcely shining; left valve with 

 one or two compressed pseudocardinals, the two often grown 

 together, with two curved, remote laterals ; right valve with 

 two elongated pseudocardinals. the lower the larger, and one 

 lateral ; muscle scars shallow ; nacre bluish-white, a little thick- 

 er in front. 



Length of type 48, height 36, diam. 20 mm. 



Length 79, height 52, diam. 28 mm. 



Uruguay River and its affluents ; Parana River, southern 

 Brazil. 

 ■ Unio fontainiana d'ORp.iGXY, Ouer. Mag., 1835, P- 36. 



