ZONITIDAE 



67 



MESOMPHIX FRIABILIS (W. G. Binney) 



So closely related to Mesomphix cupreus is Mesoinphix 

 friabilis that the collector may have difficulty in telling the two 

 apart. However, shells of the two species, each almost 1 inch 

 (24 mm.) in diameter, may be dis- 

 tinguished by certain general char- 

 acteristics. In friabilis the shell is 

 thinner and more brittle than in 

 cupreus. The spire of friabilis is 

 higher, the height of the shell usu- 

 ally being more than two-thirds and 

 sometimes as much as five-sixths its 

 diameter. In friabilis, the aperture 



is large and round, rather than expanded transversely, and the 

 umbilicus is smaller than that in cupreus. A feature which will 

 usually separate the two species as found in Illinois is that in 

 friabilis the apical or nuclear whorls are hyaline and not eroded, 

 while in cupreus these whorls have the cuticle removed. The 

 color of the friabilis shell is smoky horn with reddish tones near 

 the aperture. The interior of the aperture is violet or purplish. 

 Altogether, this is a handsome shell. 



Mesomphix friabilis lives in moist localities. It is a rare 

 species in Illinois, and only three places are at present known 

 where it has been found. These locations are on the Wabash 

 River near Mount Carmel in Wabash County, near Athens in 

 Menard County and south of Marion in Williamson County. 



The animal, which is a bluish-slate color, resembles that of 

 Mesomphix cupreus in form. 



William G. Binney, writing in 1885 of the snails of North 

 America, remarked upon the presence of friabilis in southern 

 Illinois. "The species belongs to the Interior Regions, but 

 reaches its greatest development in the vicinity of Wabash 

 County, Illinois. I have also received it from Indiana, from the 

 northern and northeastern counties of Kentucky, and from 

 Franklin County, Tennessee." 



Though rare in most parts of Illinois, friabilis is abundant 

 in southern Indiana. The finest specimens of this very delicate 

 shell have been collected in Indiana from the cypress swamps 

 in Knox County and from localities in Gibson County, where 

 the shells attain a full inch in diameter. 



