ed i 
118 Mr. Barnes on the Genera Unio and Alasmodonta. — 
muscular impression compound, hinge with two® teeth i in 
each valve; the Cardinal one, short, irregular, simple or 
divided into two, substriated ; the other elongated, com- 
pressed lateral, extending beneath the ee rang 
exterior. 
1&2, Generally, but not always when young. 
3, Others consider the divisions as separate teeth, 
Divisions. 
A. Cardinal teeth direct. 
B. Cardinal Teeth, Oblique 
Sections. 
*Cardinal teeth, very thick. 
A ** Cardinal teeth, moderately thick. 
*** (‘ardinal teeth, small. 
B { **** Cardinal teeth, broad, compressed. 
*%*** Cardinal teeth, narrow, compressed. 
* Cardinal teeth, very thick, direct. 
Species. 
a. sone 
6. outs 
’ Shell very thick, tumid ; Cardinal teeth, ary ‘angala- 
_ ted; Posterior cicatrix, deep, ro ugh. 
Unio Crassus. Mr. Say. 
Unio Crassidens. MM. Lamarck. 
Mya ponderosa ! Mr. aeure p. di. 
Mr. Say’s Amer. Conch. pl. 1, fig. 8 
Habitat. The Ohio, Mississippi, and the Lakes. 
Diameter 2°4 Length 3-2 ~— Breadth 4°8 inches. © 
My Collection. 
1. Unio Crassus. Fig. 1. 
Shell oval, ponderous, rounded behind, angulated before; 
Epidermis blackish b brown; surface waved. Cardinal 
tooth deeply sulcated; anterior cicatrix wrinkled and 
striated ; Naker pearly white and iridescent. 
Remarks.—The varieties of this shell are numerous, and 
they differ considerably i in form and surface. In some, the 
beaks are large, prominent, re-curyed, projecting backwards 
ee ee ae 
