1238 DIPr.ODON 



the rivers of South America. The beaks are very much eroded. 

 If they were perfect in the specimen, their character would, 

 I think, prove the truth of this suggestion. The character of 

 the cardinal teeth is similar to some of the South American 

 species. In the left valve it is treble, the anterior division be- 

 ing very small, the middle one being the largest. In the right 

 valve the cardinal tooth is double. The anterior cicatrices are 

 so confluent as to show no disposition to be separated. There 

 is no appearance of this specimen ever having had rays, but 

 it is very far from being a perfect individual, and young and 

 perfect ones may be rayed." 



DiPLODON BESKEANUS (Dunker). 



Shell small, trapezoidal, subinflated, subsolid, inequilateral 

 with rather low beaks, which are but little inflated, their sculp- 

 ture radial ; posterior ridge moderate, ending in a blunt point 

 behind near the base, above it on the posterior slope there is a 

 wide, shallow, radial depression, which ends in an emargina- 

 tion along the truncated border ; dorsal line slightly curved, 

 high behind ; anterior end much narrowed and rounded ; base 

 line nearly straight ; surface finely, concentrically striate ; epi- 

 dermis dark olive or olive-green, scarcely shining; left valve 

 with a lamellar pseudocardinal and a vestige of another below 

 and in front of it, with two delicate, remote laterals ; right 

 valve with two long pseudocardinals, the upper small, and 

 one lateral ; dorsal scars few, adductor scars small and super- 

 ficial ; nacre bluish-white, somewhat iridescent. 



Length 38, height 25, diam. 15 mm. 



Brazil. 

 Unio beskeaniis Dunker, Zeits. fiir Mai., V, 1848, p. 182. 

 Mar gar on (Unto) beskeaniis Le.a, Syn., 1870, p. 61. 

 Diplodon beskeanns Simpson, Syn.. 1900. p. 875. 



So far as I know this species has never been figured. There 

 is in the Lea Collection a single shell labeled Unio beskeanus 

 Dunker and presented by Dr. Dunker under that name, and 

 from it T have drawn the above description. It is decidedly 

 trapezoidal, being much wider behind than in front; the beaks 



