86 



ENDODONTIDAE 



Genus DISCUS Fitzinger 



The genus Discus embraces a group of small land snails of 

 a brownish or coppery color. In shells of this genus, the spire 

 is depressed, the height of the shell being about one-half the 

 diameter. The umbilicus is wide and deep, and the surface is 

 sculptured with distinct, sharp ribs arranged diagonally on the 

 shell. Two species of this group live in Illinois. 



Key to Species 



Shell with 4 whorls; umbilicus narrow. . . .cronkhitei anthonyi, p. 86 

 Shell with 6 whorls; umbilicus wide patulus^ p. 87 



DISCUS CRONKHITEI ANTHONYI (Pilsbry) 



The shell of Discus cronkhitei anthonyi is about one-fourth 

 inch (6 mm.) in diameter. It has 4 w^horls and a deep umbilicus 

 that exhibits all of the whorls from the base to the apex. The 



color is brownish horn, often coppery. 

 The animal has a blackish body 

 and a whitish foot. 



This variety appears to be con- 

 fined to the northern half of Illinois, 

 no specimens having been seen from 

 regions south of Fulton County. Its 

 habitats are largely in the river valleys 

 on floodplains, where it is found under 

 started bark, forest debris and stones. 

 Maple, oak and elm appear to be the 

 predominant vegetation in these habi- 

 tats frequented by anthonyi. 



Through all of its range anthonyi 

 evidences little variation. The typical 

 form of cronkhitei, of w^hich species anthonyi is a race or variety, 

 lives in the Rocky Mountain region west to California and 

 southward to Arizona. 



Discus cronkhitei anthonyi is a characteristic land snail 

 widely distributed over most of North America, the extreme 

 ranges of distribution including Ontario and Manitoba, in 

 Canada, and the state of Arizona, in the southern part of the 

 United States. 



