SPIIiERIUM. 449 



Genus VELORITA, Gray. 



Shell cordate, triangular, thick, solid, covered with an 

 epidermis. Hinge with three cardinal teeth in each valve, 

 the front in the right, and the hinder in the left valve 

 smallest ; lateral teeth large, very finely striated, the anterior 

 very large, angular, the hinder elongate and compressed. 



Ex. V. cyprinoides, Gray, pi. Ill, fig. 2, 2, a. 



The shells of Velorita are very solid, and covered with a 

 green, polished epidermis. One of the two species described, 

 V. cyprinoides, is from the rivers of Japan. 



Species of Velorita. 

 cyprinoides, Gray. recurvata, Valenc. 



Genus SPH^ERIUM, Scopoli. 



Siphons separate, diverging into two nearly equal tuhes. 



Shell equivalve, thin, ohlong, cordate, equilateral, more 

 or less inflated, smooth, or concentrically striated. Hinge 

 with two moderately- diverging cardinal teeth in each valve, 

 the front of right valve, and the hinder of left valve 

 smallest; lateral teeth elongate, compressed, smooth, of 

 right valve double, of left valve simple. 



Syn. Nux, Humph. Cornea, Mtihlf. Cyclas, Brag., 

 not Klein or Link. Amesoda, Rqfin. Spheeriastrurn, 

 Bourg. Cyrenastrum, Bourg. Corneocyclas, Ferus. 



Ex. S. lacustre, Mailer, pi. Ill, fig. 3. Shell, S. cor- 

 neum, Linmcus, fig. 3, a, 3, b. 



This genus differs from Musculium in the siphons, which 



