Occasional Papers of the Museum of Zoology II 
ness, as a matter of fact his figures of that species are not at 
all like trapezoides, but his figure No. 25 has almost exactly 
the outline of crassidens. Crassidens resembles Scalenaria 
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, he 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. 
Amblema Rafinesque, *19, p. 427; ’20, p. 314 (no type named). 
Crenodonta Schlueter, ’36, Simpson, ’ooc, 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- 
