274 



Compared to the C.falalis, this shell is more inflated and the 

 beaks are dissimilar. 



Found in company with the C. rosacea. 



6. CvcLAS GRACILIS Nohis. Bost. S. N. H. Proc. iv. 156. 



Cabinet of Prof. C. B. Adams and of T. Prime. 



Shell. Vide Bost. S. N. H. Proc. iv. 156. 



Locality. Ohio, (Adams.) 



In outline this shell is not very different from the C. similis ; 

 otherwise, however, they are not at all alike. 



The foreign analogue seems to be the C. rivicola of Europe. 

 One specimen of this species was kindly lent to me by Prof. C. 



B. Adams for description ; subsequently I obtained one myself 

 through Mr. Whittemore ; it seems to be quite rare. 



7. CrcLAs coNSTRicTA Antliomj. Anthony Cat. 1853. 



Cabinet of the B. S.N. H. 



Shell. Somewhat inflated, elongated, anterior margin rounded, 

 posterior one abrupt, inferior one straight, broken in the middle 

 by a stricture in the valves, causing a furrow up the better half 

 of the shell ; beaks somewhat prominent, not large ; lines of 

 growth very light and regular. Color greenish yellow. Hinge 

 margin very straight. Cardinal teeth united, prominent. Late- 

 ral teeth not prominent, rather elongated. Interior light blue. 



Lat. 0.55; long. 40 ; diam. 0.30 inches. 



Locality. Ohio, (Anthony.) 



This species is distinct from any on account of the peculiar 

 break in the outline of the inferior margin. Compared to the 



C. gracilis^ the beaks are less prominent and the margins are 

 less rounded. It differs from the C. transversa in being less 

 broad and in the more equal proportions of the anterior and pos- 

 terior extremities. 



8. Cyclas transversa Say. Descrip. of Terr, and fluv. 

 Shells. 1829, 30, 31. 

 Cabinet of the B. S. N. H. 

 Shell. Transversely oblong, subovate subinequilateral, anterior 



