54 



periorly ; epidermis almost smooth, brown ; api- 

 ces prominent, truncated ; nacre white, irides- 

 cent ; lamellar tooth scarcely straight ; breadth 4 

 diam. of the length axis % of the breadth. 



Var. 1. maculata with some square 

 black spots, scattered. 



Var. 2. sulcata with a slight longitu- 

 dinal depression. 



Common in the Ohio, near Steubenville, Ma- 

 rietta, &c. ; length one to three inches ; it chiefly 

 differs from the preceding species in its form, 

 its lamellar tooth somewhat curved, &c. ; animal 

 pale yellow; muscular impressions profound; 

 the fossule forms a fourth impression, which is 

 strongly marked. 



Eighth Genus AMBLEMA, 



Shell oval, elliptical or square, very inequila- 

 teral; axis lateral, posterior; apex lateral, ob- 

 lique, almost superior ; ligament straight ; lamel- 

 lar tooth vertical ; cardinal tooth wrinkled, late- 

 ral at the apex ; three muscular impressions, 

 Animal similar to the Pleurobema, 



