104 



PUPILLIDAE 



VERTIGO MORSEI Sterki 



The largest species of the genus Jertigo found in Illinois is 

 morsei, the dark brown shell of which measures nearly one- 

 eighth inch (2.5-3.0 nim.) in height. This shell is cylindroid 

 in shape and has 6^/^ well rounded whorls with 

 deep sutures. The whorls increase regularly 

 in height from apex to base. The aperture 

 is rounded, and the middle of the outer lip is 

 deeply indented. 



Vertigo morsei usually has 7 or 8 folds and 

 lamellae in the aperture: a large parietal la- 

 mella, a smaller angular lamella and a large 

 columellar lamella with a smaller lamella be- 

 low it, a very small basal fold, and an upper 

 and lower palatal fold with sometimes a third 

 fold above the upper fold. The size of the 

 shell and the 2 or 3 lamellae on the parietal wall easily dis- 

 tinguish this species from others of the genus. 



This species is known in the recent fauna of Illinois only 

 from near Joliet, Will County. As a Pleistocene fossil it has 

 been found in a number of places. Geologically it is one of the 

 oldest living species in Illinois. 



The geographical distribution of Jertigo jiiorsei is very 

 peculiar. It has been found only in New Jersey, Michigan, 

 Ohio, Indiana and Illinois. In Ohio it has been reported from 

 two localities, one a marl deposit. In Indiana, where it appears 

 to be abundant in the living fauna, there are records from three 

 counties. 



Its habitat appears to be most often near the shores of lakes. 

 The name given this species is in honor of Dr. Edward S. 

 Morse, one of the early students of land shells, who began his 

 career in Maine. Dr. IMorse was an excellent artist and made 

 all of the figures for his conchological papers. It is noteworthy 

 that he was also the artist for Dr. William G. Binney's works 

 on American land and freshwater mollusks. 



.'\n inadvertent step may crunch the snail 

 That crawls at evening in the public path, 

 But he that has humanity, forewarned, 

 Will turn aside and let the reptile live. 



— William Cowper, The Task 



