B 

 284 GENUS OLYGYRA. (Jutie. 



the shell; foot not broader than the body; tail rounded^ 

 or somewhat acute; operculum simple, not spiral, yellow- 

 ish brown, minutely granulated. 



This species we found in great numbers on what are 

 called Oystershell Hammocks,* near the mouth of the 

 river St. John, East Florida, in company with Polygyra 

 septemvolva. When in motion, the tentacuia are elevated 

 and depressed alternately, as if feeling the Way. , 



This shell is certainly a Linnaean Helix, but accord- 

 ing to the improvements which have been made in Con- 

 chology, since the time of the Swedish naturalist, by Mr* 

 Lamarck, and other systematists, it is at once excluded 

 from that genus and its congeners, by having but two 

 tentacuia, and by its operculated aperture; with the ge- 

 nus Cyclostoma, as it now stands, our shell has more af- 

 finity than it has to any other, but a very distinct generic 

 character is observable in the aperture, which is not orbi* 

 cular as in Cyclostoma, but is almost semi-orbicular, 

 greater in length than in breadth, and the lips widely dis^ 

 united. In addition to the characters usually given of 

 the animal of Cyclostoma, Mr. Cuvier remarks that the 

 tentacuia are terminated by obtuse tubercles; no such ap- 

 pendages are annexed to the corresponding members of 

 this animal. Upon these considerations I have thought 

 proper to construct the present genus. 



* These are elevated knolls of oyster shells mixed with earth, which rise 

 by an abrupt acclivity on all sides, from the salt marshes in that country, to 

 the elevation of fifteen or twenty feet; they exliibit to the eye the appearance 

 of old oyster beds, (Oyster .Rocks) which, owing to their compactness, have 

 resisted the action of the waters for centuries, while the more yielding earth 

 around them has been washed away to its pl*esent level, by imperceptible de-* 

 grees. 



