PUPILLIDAE 



105 



VERTIGO OVATA Say 



Although the shell of Vertigo m or set resembles that of Fer- 

 tigo ovata in the form and position of the folds and lamellae 

 of the aperture, the two may be distinguished by a difference 

 in size and in the number and shape of the 

 spire whorls. The shell of ovata measures 

 somewhat more than one-sixteenth inch (2 

 mm.) in height. It has 5 whorls, which are 

 proportionately wider than those in morsel 

 and increase in height more rapidly from 

 apex to base. The ventricose form of the 

 last or body whorl is also different. Vertigo 

 ovata is somewhat amber colored. 



The habitat of the snail Vertigo ovata 

 is in moist places under sticks and debris. It 

 is most abundant on stream floodplains, but 

 it has been found also in forests on the bluffs that border rivers. 



This species, scatteringly distributed over Illinois, has been 

 reported from Fulton, McHenry, Cook, Menard, Winnebago, 

 Washington. Edwards, Jackson and White counties. However, 

 it is common only from the vicinity of Rockford, in Winnebago 

 County, and of Albion, in Edwards County. Winnebago County 

 is its most northern Illinois locality, Jackson its most southern. 



VERTIGO VENTRICOSA (Say) 



The shell of Vertigo ventricosa differs from that of Vertigo 

 ovata in size and shape. It is a trifle smaller, measuring about 

 one-sixteenth inch (1.75 mm.) in height. The glossy, light 

 brown or auburn-colored shell of 4 whorls 

 is often translucent. It has a lamella on the 

 columella, a basal fold and an upper and a 

 lower palatal fold. It has one parietal la- 

 mella. These characteristics distinguish it 

 from the shell of ovata. 



At present only one Illinois locality is 

 known where ventricosa may be found. 

 Specimens are known from near Rockford, 

 Winnebago County, but even in that locality 

 this species is rare. 



