106 HELICID^. 



reflected, not flattened, with sometimes a slight thick- 

 ening on the inner side near the base ; umbihcal region 

 indented. 



Extreme transverse diameter, three-fourths of an mch. 



Geographical Distribution. Inhabits Ohio, and 

 the western part of Pennsylvania, and may probably be 

 found in all the States bordering on the Ohio river. 



Remarks. A very well marked species, distinguished 

 chiefly by its triangular mouth and elevated spire. The 

 volutions are usually about six, rounded, or convex. The 

 shell is rather thin, and the lip but narrowly reflected. 

 Some individuals resemble M. elevata, Say, as is mention- 

 ed in the remarks on that species. The color of all the 

 thinner shells of this genus appears darker when the 

 animal is retracted into the shell, and this species has 

 then, sometimes, a purplish tinge. The shell varies in 

 being more or less elevated ; in some individuals the spire 

 is much flattened. It difiers greatly in size also, some 

 perfect shells not attaining more than one half the size of 

 others. Some persons have thought that ff. clausa, 

 Say, is a small variety of this shell ; but the roimded aper- 

 ture, which is a constant character in that shell, precludes 

 that supposition. The specimen figured in the plate is a 

 rather large one. 



The animal of this, and many other species, is often 

 overrun with great numbers of Acari, resembling Acarus 

 limacum of Europe. There appears to be at least two 

 species of them. They are very minute, flesh colored. 



