ZONITIDAE 69 



Genus RETIN ELLA (Shuttleworth) Fischer 



Snails of the genus Retinella have small hyaline shells. In 

 none of the species of Retinella does the shell greatly exceed 

 one-fourth inch (6.5 mm.) in diameter. The shells of these 

 snails are glassy and shining; after the animal has been removed, 

 they appear almost as though varnished. They appear black 

 when the animal is present. They range from light brown to 

 creamy white in tint, the color differences pertaining to indi- 

 vidual shells rather than to all the members of a species. 



Snails of the genus Retinella usually live in woodlands of 

 oak, hickory, maple and elm. Some species are solitary in habit, 

 but the majority live in colonies, and usually a number of speci- 

 mens may be collected from one piece of rotting timber. 



The four species of Retinella occurring in Illinois may be 

 known from all of the other small species of zonitoids by the 

 presence of regular, radiating impressed lines extending from 

 the suture to the base of the body whorl. The impressed lines 

 are parallel with the growth lines, but are evenly spaced, with 

 growth lines between. 



The animal of Retinella is bluish or blackish in color. 



Key to Species 



1. Base of shell flattened; umbilical region indented and having 



a very small perforation indentata, p. 71 



Base of shell not flattened; distinct umbilical opening, p. 70. . 2 



2. Umbilical opening elliptical wheatleyi^ p. 70 



Umbilical opening round, p. 70, fig. C 3 



3. Shell with impressed radiating lines widely and regularly 



spaced rhoadsi^ p. 70 



Shell with impressed radiating lines close together 



electrina, p. 69 



RETINELLA ELECTRINA (Gould) 



The shell of Retinella electrina, less than one-fourth inch 

 in diameter (5 mm.), is over twice as broad as high. Yellowish 

 in color, it has a shining, glassy surface, upon which the radi- 

 ating impressed lines occur rather close together. The shell has 

 4 whorls, a rounded base and a round, wide and deep umbilicus, 

 fig. A, page 70. 



Retinella electrina, also known as Vitrea hammonis and 



