CONCHACEA. MOLLUSC A. CYCLAS. 73 



markably broad across the beaks, which are but slightly elevated ; 

 color dark chestnut-brown, within bluish. The young shell is 

 thin and compressed, the hinge margin nearly a straight line, the 

 extremities truncated so as to give the shell a quadrilateral form ; 

 and the color is a light lemon-color, or honey-yellow. The 

 intermediate specimens exhibit all the gradations of shape or color 

 between the old and young. Surface at every stage regularly 

 wrinkled concentrically, with strongly raised, sharp lines of 

 growth, and generally a more conspicuous wave marking the 

 former year's growth of the shell ; beaks usually eroded. Hinge 

 with minute, very oblique cardinal teeth, the lateral ones distinct, 

 strong and white. Length T \ inch, height -J inch, breadth | 

 inch. 



Found in the larger ponds and rivers, especially along the 

 muddy banks of the Connecticut. 



This species is closely allied to the C. rivicola of Europe in shape 

 and size ; its raised concentric striae, however, appear to be much 

 more prominent. It may always be distinguished by these conspicu- 

 ously raised lines, for they are exhibited by no other American species 

 in so great a degree. Several other species are described as having 

 them, such as are named under the, synonyms ; but they are probably 

 all of them varieties of this species. The young, differing widely as it 

 does from the adult, has been commonly received in our cabinets as 

 Say's C. rhomboidea. A specimen one fourth of an inch long would 

 answer very well to his description. What the true rhomboidea is, I 

 have not yet been able to satisfy myself. The two species of Lamarck, 

 also, I believe to be varieties of this shell ; and very probably his C. 

 striatlna also. 



CYCLAS PARTUME'IA. 



Shell rounded-oval, sub-equilateral, narrowest anteriorly, some- 

 what angular behind ; thin and fragile ; valves very convex, mi- 

 nutely wrinkled by lines of growth, and obsoletely radiated ; light 

 horn-color ; beaks elevated. 



FIGURE 54. 

 State Coll., No. 203. Soc. Cab., No. 1699. 



Cyclas partmn&a SAY ; Journ. Acad. Nat. Sc., ii. 380. 

 Cyclas cornea, yar. 2, 3. LAM.; Jin. sans Vert., vi. 2G8. 

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