06 



PUPILLIDAE 



VERTIGO ELATIOR Sterki 



The elatior species of Vertigo is larger than Vertigo ventri- 

 cosa. The brown shell of elatior, measuring over one-sixteenth 

 incli (2.25 mm.) in height, has 5 whorls, one 

 more than is present in ventricosa. It is 

 more elongated and more nearly cylindrical. 

 The folds and lamellae in the aperture are 

 the same in number, 5, as in ventricosa. but 

 the basal fold is larger, and the palatal folds 

 are placed on and merge into a strong callus 

 or thickening within the outer lip. 



Curiously, in Illinois Vertigo elatior is 

 known only from Rockford, Winnebago 

 County, where Vertigo ovata is found. It 

 is rare in the living fauna, but as a Pleisto- 

 cene fossil, under the name of Vertigo loes- 

 sensis F. C. Baker, It is very abundant and widely distributed 

 in Illinois and other parts of the Middle West. 



VERTIGO TRIDENTATA V^olf 



The small amber-colored shell of Vertigo tridentata is little 

 more than one-sixteenth inch (2 mm.) in height. It has 5 smooth 

 whorls. The small number of folds and lamellae distinguishes 

 this species from the other vertigos 

 of Illinois. The two figures illus- 

 trate some of the individual varia- 

 tions within the species. 



The habitat of Vertigo triden- 

 tata is in grass or weeds. It has 

 been observed clinging to stalks of 

 weeds as high as 3 feet from the 

 ground. 



Vertigo tridentata has been col- 

 lected in Will, La Salle, Champaign and Fulton counties. Its 

 first known habitat was In Fulton County, where it was dis- 

 covered by an Illinoislan, John Wolf, about 1870. 



The vertical line beside the smaller figure Indicates the height 

 of the specimen represented. The shell represented by the figure 

 at the right is proportionately larger. 



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