Diri.onoN 1279 



Section Cyclomya s. s. 

 DiPLODON PATEJ.LoiDES (Lea). 



Shell unevenly rhomboid, short, somewhat compressed, 

 rather solid, slightly inequilateral ; beaks moderately full and 

 elevated above the dorsal line, sculptured with radial bars ; 

 dorsal line curved in in front of the beaks and upward behind 

 them ; posterior ridge full and rounded, ending" behind in a 

 blunt point just below the median line, above this point the 

 shell is obliquely trvmcated ; base swelled at and behind the 

 middle ; anterior end narrowed and pointed ; surface rudely 

 and unevenly, concentrically sculptured, showing traces of 

 radial sculpture; epidermis dark brown, scarcely shining; left 

 valve with two compressed, ragged pseudocardinals, the hinder 

 small, and two curved laterals ; right valve with two pseudo- 

 cardinals, the upper small, and one lateral; laterals granular; 

 muscle scars well marked ; nacre white, somewhat silvery, 

 thicker in front. 



Length 75, height 59, diam. 28 mm. 



Amazon River. 

 Unio patelloides Lea, Pr. Ac. N. Sci. Phila., IV, i860, p. 89: 



Jl. Ac. N. Sci. Phila., V, 1863, p. 383. pi. xliii, fig. 291 ; Obs., 



X, 1863, p. 19, pi. xuTi, fig. 291. 

 Margaron (Unio) patelloides Lea, Syn., 1870, p. 56. 

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



A rudely sculptured species with distinct traces of radial 

 grooves, with a rich brown epidermis. The pseudocardinals 

 are more compressed than those of D. funebralis ; it is sharper 

 in front and behind and not so swollen in the post-basal region. 



Diplodon PER.iiFORMis (Lea). 



Shell irregularly obovate, subsolid, subinflated, inequilateral, 

 with only moderately full or elevated beaks, whose sculpture 

 is radial ; posterior ridge well defined and subangular, ending 

 behind in a point a little above the median line ; above this 

 point the shell is obliquely truncated ; anterior end narrow and 

 rounded; base very full just behind the middle; surface very 

 slightly, concentrically sculptured ; epidermis bottle-green ; left 



