232 



subangular, generally distinct, and sometimes separate from the 

 body whorl, and usually fiirnislied with teeth. 



Ohs. The shells belonging to this genus have been divided, with 

 much propriety, from the Linngean genus Turho ; they inhabit 

 moist places, under the bark of trees, under stones, moss, &c. ; many 

 of them are sinistral. 



Helicina.* — Shell subglobular ; spire depressed, or but little 

 elevated ; aperture semiorbicular, modified by the preceding volu- 

 tion ; base with a more or less obvious callosity covering the um- 

 bilicus ; labrum acute or a little reflected; columella at base alittle 

 prominent, and joined to the labrum at an angle ; operculiun homy, 

 iind with concentric elements. 



Animal terrestrial, globular, subspiral ; head rostrated ; rostrum 

 bilabiated, at the tip end shorter than the tentacula, which are two 

 in number, filiform, and have the prominent eyes at the exterior 

 part of their base, upon a tubercle ; the organs of respiration as in 

 Gyclostoma; the branchial cavity communicates with the atmos- 

 phere by a large slit ; foot simple, with an anterior marginal groove. 



Ohs. The general appearance of the shell resembles much that 

 of a Helix, but the base of the columella is a little prominent, and 

 the locality of the umbilicus is more obviously covered with a cal- 

 lus. But the most striking difi"erence is in the animal, which in 

 Helix has the eyes at the tip, of the superior pair of tentacula, 

 whereas in Helicina they are at the exterior base of the only pair ; 

 the operculum of the latter is also a sufficient distinction. 



Lamarck formerly united several species under this genus that 

 he has since very properly separated under the name of Rotella, 

 ( Pitonillus, Montf.,) as being inhabitants of the ocean, with a 

 much dilated basal callus. This union led me to form my genus 

 Oligyra for the reception of one of the following species, well 

 knowing it could not be naturally congeneric with the Linnsean 

 Troclius vestiarius, the type of that genus. 



In the Zoological Journal, for 1824, Gray has described fifteen 

 species, which he disposes in several minor groups ; but Ferrussae 

 states, that he possesses from twelve to fifteen species which seem 

 to be unknown to Gray, some of which he could not refer to either 

 of those groups. Notwithstanding the variations and transitions of 

 the species, it may be found convenient and even natural to sepa- 

 [* Am. Con. v.— Ed.] 



