A. BIVALVES. 



1. Cyclas. 



2. Anodon. 



3. Unio. 



4. Mysca. 



I. CYCLAS. 



Shell bivalve, equivalve, orbicular or oval, closed all 

 round. Hinge with two minute divergent primary 

 teeth in each valve ; and an elongated lateral one 

 on each side, which is doubled in one of the valves. 

 Ligament external. 



* Somewhat orbicular and equilateral. 



1. CYCLAS rivicola. Shell rather convex and opake, 

 with regular close-set transverse striae. 



Cyclas rivicola. Turton, Dith. p. 248. t. 11. /. 13. 



Lamarck, v. p. 558. 



Cyclas cornea. Draparn. p. 128. 1. 10. /. 1 3. 

 Tellina cornea. Wood, pL 46. /. 3. 

 Cardium corneum. Montagu, p. 86. large var. 



