82 



ZONITIDAE 



VENTRIDENS DEMISSUS (Binney) 



The snail Ventridens demissus must not be confused with 

 immature specimens of Ventridens ligerus, which it somewhat 

 resembles. As the fully matured whitish shell of demissus 



usually measures considerably less 

 than one-half inch (10 mm.) in 

 diameter, it is smaller than that 

 of ligerus. Small differences in 

 the proportion and shape of the 

 shells further serve to distinguish 

 the two species. In demissus, the 

 spire of 7 whorls is somewhat 

 more depressed than the spire of 

 ligerus with its 6 whorls. In ligerus, the first 3 or 4 whorls are 

 wider than the corresponding whorls in demissus. The small 

 aperture in demissus is crescent shaped; the larger aperture in 

 ligerus is shaped like a half moon. 



The animal of demissus differs from that of ligerus in being 

 whitish or slaty, and in having blue head and eye peduncles. 



Authentic records of this rare species are known from but 

 two Illinois counties. In Shelby County the shells have been 

 found on the blufiFs of the Kaskaskia River, and in Effingham 

 County on a railroad right of w^ay. It is a southern species 

 which has apparently migrated into Illinois from Kentucky or 

 Indiana. 



Two other species of Fentridens have been reported from 

 Illinois by collectors. Ventridens intertextus (Binney), once 

 known as Gastrodonta intertexta, has been reported from Ver- 

 milion County by Marsh, but almost certainly it does not live 

 there, for this record has not been verified after 20 years of 

 collecting by many other students. Hinkley records it from 

 White County, and since the species lives in Posey County, 

 Indiana, just across the Wabash River, it would be logical for 

 it to inhabit eastern Illinois, but thus far subsequent collections 

 from this region have failed to include intertextus. Careful 

 collecting in White County opposite New Harmony, Indiana, 

 has failed to locate even a single dead or bleached shell. The 

 record of Gastrondonta gularis from northern Illinois by Cal- 

 kins is very doubtful. This species, now known as Ventridens 

 gularis, has not with certainty been found north of Tennessee. 



