280 



whole shell is of a different texture. This is a beautiful species, 

 as yet very rare, however. 



18. CYCLAS DENTATA Haldeman. Proc. Ac. Nat. Sc. i. 103. 



Cabinet of the Ac. Nat. Sc. 



Shell. Large, ventricose, somewhat equilateral ; inferior and 

 anterior margins rounded ; posterior one somewhat angular ; 

 beaks large, well rounded, distant, not very prominent ; hinge 

 margin nearly straight ; cardinal teeth single, well visible ; 

 lateral teeth not prominent, of growth not deep, regular ; color 

 olive-green, with a dark streak, of little width, some distance 

 above the inferior margin. 



Long. 0.50 ; lat. 0.40 ; diam. 0.36 inches. 



Locality. Oregon, (Nuttall.) 



The young shell differs from the adult ; it is much more 

 elongated and more heavily striated ; it is less inflated ; the 

 beaks are neither as large nor as tumid ; the color is the same. 

 This species bears a strong resemblance to the C. albula, but it 

 is somewhat more full ; the posterior extremity is not so angu- 

 lar ; its anterior extremity is more rounded, and the beaks are 

 more large and tumid. It is rather more full and less heavily 

 striated than the C. acwninata. It differs from C. similis, in 

 being shorter, more equilateral, less heavily striated, and of 

 a different color ; the young is more full and less elongated than 

 that of C. similis. 



19. CYCLAS ELEVATA Haldeman. Proc. Ac. Nat. Sc. 1841, 



53. De Kay, 225. 



Cabinet of the Ac. of Nat. Sc. 



Shell. Ovate, orbicular, nearly spheri- 

 cal, strong, cavity large, equilateral, mar- 

 gins well rounded ; beaks central, slightly 

 inclined towards the anterior, lapping 

 over the outline of the shell, large, tumid, 

 approximate ; hinge margin slightly curv- 

 ed ; cardinal teeth united, prominent; 



lateral ones elongated, large ; surface smooth, striation light 

 and regular ; color brownish olive, greatly varied by zones of a 



