50 ^ POLYGYRIDAE 



^'^"POLYGYRA ZALETA (Binney) 



The common Polygyra zaleta greatly resembles the white- 

 lipped snail, Polygyra albolabris, and particularly the variety 

 dentata. Its horn-colored shell is much more globose than that 

 of albolabris, which is wider than it is high. The species zaleta 



has also a distinct, rather mas- 

 sive denticle on the parietal wall 

 which is absent in albolabris al- 

 bolabris and only very feebly de- 

 veloped in albolabris dentata. The 

 shape of the shell and the parietal 

 denticle separate the two species 

 zaleta and albolabris. 

 The only variation among individuals of the species zaleta 

 in Illinois is in the size of the shell, the extremes of which are 

 less than 1 inch and more than Ws inches (24 and 29 mm.). 

 This variation, however, occurs in the same colony and is to be 

 considered simply variation in different individuals. 



The animal resembles that of albolabris in form. It is 

 grayish-brown or blackish in general color, lighter near the foot 

 and at the posterior end. The eye peduncles are long, slender 

 and black. The animal is never so light colored as that of 

 albolabris. 



Polygyra zaleta is widely distributed over Illinois and, as 

 with Polygyra albolabris, this distribution is very sporadic. It 

 is most abundant in the eastern and southern parts of the state, 

 where it lives in ravines of the smaller river tributaries as well 

 as on the bluffs of the larger rivers. It prefers regions of oak, 

 elm and hickory where there is much debris on the ground. 

 Singularly, the species is not known in the Mississippi Valley 

 north of Calhoun County. 



This species was once named Polygyra exoleta Binney, as 

 explained by William G. Binney. "When Dr. Binney (Dr. 

 Amos Binney, father of William G. Binney) published the first 

 description of this snail, in 1837, he adopted, without examina- 

 tion, the name zaleta, which he found applied to it in some 

 cabinets, and which he then supposed had been applied by Mr. 

 Say. Finding no description of it, he subsequently applied the 

 name, exoleta, originally suggested, no doubt, by the idea that 

 the species is an old, or superannuated form of albolabris." 



