HEL1CINA. 357 



REMARKS. This shell is found abundantly in a fossil 

 state, in the post-tertiary formation of the West ; and 

 it is not certain that it now exists in a recent state. 

 A different opinion was expressed in the first volume, 

 (p. 183 - 4) ; but we have been induced by subsequent 

 observations to adopt a contrary conclusion, as will be 

 seen in the remarks upon the preceding species. The 

 shell is well distinguished from If. orUculata by its more 

 depressed form, its carinated suture and the smoothly 

 curved gibbous form of the lip at its base, instead of the 

 decided angle of H. orUculata. The peculiar suture, in 

 every example I have seen, constantly marks the species. 

 A single specimen of a recent shell has come under obser- 

 vation, in which the spire exhibits the above characters ; 

 but the aperture is different, and the history of the shell 

 is not known. Most of the land and fluviatile shells 

 inhabiting the valley of the Ohio and Mississippi, have 

 been found fossil in the bluffs of that region, under 

 the same circumstances in which this is found ; and 

 should this species prove to be extinct, it will be the only 

 land shell yet found, which has coexisted with the now 

 recent species, and has become extinct. One or two 

 fluviatile species, Limnea obrussa and yallana for 

 instance, have also become extinct. [G.] 



