DIPLODON 



1247 



to the last quarter of the length of the shell whence it again 

 ascends. The angle in which the two parts of the ventral mar- 

 gin meet posteriorly is not as distinct as in the typical speci- 

 mens collected by Spix in the Rio Sao Francisco. This reason 

 and the somewhat smaller dimensions induce me to regard the 

 specimens from the Santa Maria River as a distinct subspecies, 

 which I name santoniis." (von Ihering). 



Diplodon cllipticus santanus vok Ihkrinc, Abhandl. Senckenb. 

 Naturf. Ges., 32, 1910, p. 134. 



Diplodon yi^THiop.s (Lea). 



Shell oblong, convex, subsolid, with a straight dorsal line, 

 the posterior slope rather abruptly truncated, the basal line 

 slightly curved; posterior ridge high, subangular ; dorsal slope 

 with a few, irregular wrinkles, beaks low, rather full, their 

 sculpture not seen : surface with irregular, subsulcate sculp- 

 ture; epidermis black, scarcely shining; left valve with two 

 compressed, small, ragged pseudocardinals and two delicate 

 laterals ; right valve with two pseudocardinals. the upper very 

 small and one straight lateral ; nacre whitish, somewhat thick- 

 er in front. 



Length 53. height ly, diam. 18 mm. 



LVuguay and Paraguay Rivers; southern Brazil. 

 Unio cethiops Lea, Pr. Ac. N. Sci. Phila.. IV. i860, p. 91 ; Jl. 



Ac. N. Sci. Phila., V, 1863, P- 377^ pl- xli. fig. 285; Obs., 



X, 1863, p. 13, pl. xi,[, fig. 285. 

 Mar oar on (Unio) cethiops Lea, Syn., 1870, p. 53. 

 Diplodon cethiops Simpson, Syn., 1900, p. 877. 



T have only seen a single dead specimen, not in good condi- 

 tion, the type. The dorsal line is quite straight; the post- 

 ridge is high and subangular. the dorsal slope has a few wrink- 

 les and the epidermis is almost jet black throughout. 



Var. piiacicabanus (von Ihering). 



"Valves thick; posterior extremity rounded: lateral teeth 

 straight or slightly curved." (von Ihering). 

 Piracicaba, San Paulo, Brazil. 



