ZONITIDAE 



71 



RETINELLA INDENTATA (Say) 



The small, yellowish, glassy shell of Retinella indentata 

 measures about one-fourth inch (5 mm.) in diameter and is 

 only about half as high as wide. The impressed radiating lines 

 are equally spaced and widely sepa- 

 rated. The base is flattened, and the 

 umbilical region, which is markedly 

 indented, has only a very small chink 

 or perforation. No other shell in Illi- 

 nois has this peculiarly indented and 

 almost imperforate base. 



The animal is blue-black, and has 

 lighter shades of coloring on the mar- 

 gin and posterior extremity. 



This snail, which was first observed 

 by Thomas Say more than a hundred 

 years ago, is one of the most abundant 

 Illinois species. It may be found living 

 in almost every county in the state. It is found in the river 

 valleys, in wooded areas and in former prairie lands, associated 

 with Retinella electrina, Zonitoides arboreus and other small 

 snails. Its most favorable habitat, like that of so many other 

 small snails of the state, is in woodlands of oak, elm, maple and 

 hickory. It may be found under loose bark, woodland debris 

 and fallen limbs of trees. 



Retinella indentata is widely distributed throughout the 

 United States and parts of Canada and Mexico. Its range as 

 known at present is from Ontario, Canada, southwest to lower 

 California and central Mexico, and from the Dakotas east- 

 ward to the Atlantic states. Throughout this wide area it 

 exhibits little variation. Only one race besides the typical is 

 known in this area, and that is confined to the southern United 

 States and Mexico. 



A closely allied species, Retinella cryptomphala, is common 

 in Tennessee and Alabama but has not surely been detected in 

 Illinois, since specimens reported as cryptomphala, collected at 

 Albion, Edwards County, proved upon close examination to be 

 a variation of the common indentata. This Illinois locality is 

 far removed from the usual localities in which cryptomphala 

 lives, and the record appears to be erroneous. 



