Occasional Papers of the Museum of Zoology 1 1 



ness. as a matter of fact his figures of that species are not at 

 all like irapesoides, but his figure No. 25 has almost exactly 

 the outline of crassidens. Crassidens resembles Scalenarm 

 more than trapezoides in that the greatest diameter is at the 

 anterior third of the shell, while in trapezoides it is at the 

 posterior third. The position of the axis as given by Rafin- 

 esque is the same in Scalenaria scalenia and Bariosta pon- 

 derosa. The general shape given, "triangular or oval-trian- 

 gular/' applies better to crassidens than to trapezoides. Trape- 

 zoides would hardly be called a "thick and heavy" shell. It is 

 certainly not nearly as much so as crassidens. 



The "lamellar tooth, curved and not obliqual," and the 

 "oblique ridge ending to a point'' would seem to point to tra- 

 pezoides, but many specimens of crassidens have a well- 

 marked umbonal ridge which ends at or just above the poste- 

 rior point, and the characteristic sculpture of the disk of tra- 

 pezoides is indicated by only one word (rough), which surely 

 is not an appropriate description of it. 



The "scabrous" lamellar tooth does not apply to either spe- 

 cies, and the "many uneven wrinkles inside" are quite unin- 

 telligible. 



For these reasons ponderosus must be considered to be 

 unidentifiable, and with it goes Bariosta into the discard. 



Genus AmblEma Rafinesque, 1819 

 Type: Amblema costata Raf. '20. 



Amhlema Rafinesque, '19, p. 427; '20, p. 314 (no type named). 



Crenodonta Schlueter, '36, Simpson, 'oo<:', p. 766 (as section of 

 Quadrula) (type: Unio plicatus Say) ; Ortmann, '17, p. 245 (as genus). 



Amblema Raf., Frierson, '14*, p. 7 (type A. costata Raf.) ; Utter- 

 back. '16, p. 31; Ortmann, '18. p. 538; Walker, '18", pp. 47, 171. 



Amblema Raf. '20 originally had five species. Frierson (1. c.) 

 has designated A. costata as the generic type. This is a rec- 



