59 



thickened ; animal resembles that of the Unio. 

 This genus may be divided into three very dis- 

 tinct sub-genera. 



First Sub-Genus ANODONTA. 



No lamellar wrinkles on the hinge. This sub- 

 genus comprehends the greater part of the spe- 

 cies, viz : A. Anatina, A. cygnea, A. radiata, 

 A. marginata, SAY A. cataracta, SAY, besides 

 the two following species which I observed in 

 the Hudson river. 



ANODONTA ATBA. 



Shell ventricose, thin, smooth, elliptical, black- 

 ish; nacre white anteriorly, reddish brown, 

 iridescent posteriorly. Length diam. T 5 2 

 axis i of the breadth. Breadth does not exceed 

 six inches. 



ANODONTA CUNEATA. 



Shell slightly ventricose, thin, elliptical, at- 

 tenuated posteriorly ; epidermis wrinkled, olive 

 brown ; nacre bluish white. Length - diam. 

 axis j of the breadth. Breadth four to five 

 inches. 



