157 



beaks are also larger and more tumid ; the outline of the two 

 extremities is rather angular, whereas, in the C. cornea, it is 

 rather rounded than otherwise. 



Cyclas mirabilis. C. testa tenui, fragili, subovata, sube- 

 quilaterali, postice abruptissima, umbonibus parvis, elevatis. 

 Long. 0.41 ; lat. 0.34; diam. 0.25 inches. Hab. Georgia. 

 (Haldeman.) 



Shell very delicate, posteriorly very abrupt, beaks small but 

 tumid. Color light gray, striations not visible. 



Remarks. Comparing this species with the C. partumeia Say, 

 I find, that in the outline they are very similar ; the beaks of the 

 C. mirahilis are, however, smaller, though fully as tumid, and 

 the whole shell is rather less inflated than the C. partumeia. 



Cyclas Jayensis. C. testa pellucida, fragili, brevi, globosa, 

 subequilaterali, transverse rotundata, postice abruptissima, alba, 

 nitida, tenuiter striata, umbonibus magnis, elevatis. Long. 

 0.49; lat. 0.40 ; diam. 0.27 inches. Hah. Lake Superior. 

 (Agassiz.) 



Remarks. This shell has a slight resemblance to the C. par- 

 tumeia Say, but is posteriorly more abrupt. Cabinet of the Bos- 

 ton Society of Natural History. 



Cyclas gigantea. C. testa maxima, forti, solida, subovata, 

 complanata, equilaterali, elongata, postice abrupta, umbonibus 

 magnis non elevatis. Long. 0.70 ; lat. 0.56 ; diam. 0.39 inches. 

 Hah. Pennsylvania. 



Shell very large, probably the largest known, rather full. 

 Color, dark chestnut brown, striations light but regular, generally 

 found with beaks eroded. 



Cyclas ponderosa. C. testa magna, forti, solida, brevi, 

 subglobosa, inequilaterali, postice acuta, lineis incrementi fortiter 

 instructa, umbonibus rotundatis, approximatis. Dentes fortes. 

 Long. 0,68 ; lat. 0.54 ; diam. 0.37 inches. Hab. Lake Supe- 

 I'ior. (Agassiz.) 



Shell large, heavy, solid ; lines of growth deep and irregular. 

 Color dark brown, interior grayish white. 



Remarks. With the exception of the C. gigantea Nobis, this 

 is the largest species known. Hitherto single valves only have 



