DIPLODON 1277 



Unio acntirostris Lea, Pr. Ac. N. Sci. Phila., X, 1866, p. 34; 



Jl. Ac. N. Sci. Phila., VI, 1868, p. 270, pi. xxxv, fig. 84; 



Obs., XIII, 1869, p. 30, pi. XXXV, fig. 84. 

 Margaron (Unio) acntirostris Lea, Syn., 1870, p. 58. 

 Diplodon acntirostris SnrpsoN, Syn., igoo, p. 885. 



I am very doubtful whether this is more than a form of 

 d'Orbigny's patagonicns. I have only seen one shell, the type, 

 which is badly eroded. The teeth and nacre differ somewhat 

 from those of specimens of that species in the Lea Collection 

 and it is a little more decidedly truncate in front, but the differ- 

 ences are only of degree and there seems to be considerable 

 difference in these characters among the shells I have seen. 



Group of Diplodon quadrans. 



Shell subtrapezoid, slightly truncate in front, nearly equilat- 

 eral, greatly inflated, its greatest diameter below the beaks, 

 from which it is wedge-shaped in front and behind, solid, 

 with a decidedly rounded posterior ridge ; epidermis brownish, 

 concentrically striate; beaks full, but not high; ligament long 

 and slender; pseudocardinals large, compressed, striate, and 

 ■crenulate, double in the right valve, single in the left ; laterals 

 curved, crenulate ; beak cavities rounded ; anterior cicatrices 

 •deep, confluent ; nacre white. 



Animal unknown. 



Diplodon quadrans (Lea). 



Shell short, subrhomboid, inflated, somewhat inequilateral, 

 rather solid ; beaks full, but not very high ; posterior ridge full, 

 rounded, ending behind in a rounded point at the base ; ante- 

 rior end somewhat truncated, subangular above ; surface strong- 

 ly, concentrically striate ; epidermis dark brown ; pseudocardi- 

 nals compressed, the anterior one in the left valve small ; lat- 

 erals decidedly curved ; anterior muscle scars deeply impress- 

 ed ; posterior scars shallow ; nacre white and iridescent, thick- 

 ened in front. 



Length 93, height 68, diam. 52 mm. 



South America ( ?). 



