390 LAND AND FRESH-WATER SHELLS OF N. A. [pART IV. 



to be superposed by the animal, probably with the intention of re- 

 Fig. 743. Fig. lu. Fig. 745. taining a proper specific gravity. The apex 

 is often truncated. This species was found by 

 Mr. Thomas Nuttall, during a journey to Pitts- 

 burg. — Say. 



Figure 737 represents a tj'pieal shell and figure 743 Mr. 

 Say's variety B. 



The following is Mr. DeKay's description of 



Anculosa carinatus. — Shell short, pyramidal, thin and fragile ; 

 whorls with a distinct, elevated carina, rather suddenly attenuated to 

 the apex, which is frequently eroded ; the whorls are polished with 

 incremental stria? ascending to the edge of the carina, where they 

 become multiplied, especially on its lower aspect ; suture canaliculate, 

 by the elevated carinte ; aperture subrhomboidal ; outer lip simple, 

 angular reflected at the base ; pillar lip concave, with a broad cal- 

 lus ; outer lip above contiguous to the carina of the preceding whorl ; 

 color amber, darker towards the lip. 



Length of shell, "45 ; extreme width of shell, 'i of an inch. Length 

 of aperture, -4:0 of an inch. 



Observations. — This very remarkable species, which may probably 



form the type of a new genus, is from Lake Charaplain. My 



Fio- 746 

 thanks are due to Dr. B. W. Budd, for an opportunity of 



adding this to the state collection. I have since obtained 

 others from Cranesport, Broome County, in one of the trib- 

 utaries of the Susquehanna. These are dai'k olive-green and 

 many of them •5--6 of an inch long. An eminent conchologist pro- 

 nounces it identical with A. dissimilis, but I have not found the 

 description of this species. — DeKay. 



The figure is copied from that of Mr. DeKay. This spe- 

 cies is of protean form and substance, being either thin or 

 ponderous, large or small, carinate or smooth, with or without 

 a tooth on the columella. It is not without much study of 

 numerous individuals from many localities, that I propose to 

 unite forms which eminent couchologists have alwaj's con- 

 sidered very distinct, but I find no characters in any of the 

 so-called species here included, which do not become lost in 

 transition fonns. In certain parts of Eastern Virginia and 

 Maryland the shell attains but a small growth, becomes stunted 



