20 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 487 



anatomical characters. The differences are not striking, and the validity of the 

 genus may be questioned on biological grounds. As recognized, however, the 

 genus is Holarctic in distribution. 



Aplexa hypnorum (Linne) 1758 



Bulla hypnorum Linne 1748, Syst. Nat. Ed. 10, p. 727. 

 Aplexa hypnorum (Linne), F. C. Baker 1928, Freshwater Moll. Wisconsin, 

 pt. 1, p. 473, pi. 19, figs. 1-4. 



Whatever may be the true systematic relations of this species, the shells 

 are readily recognized by their sinistral spirals, polished surface, and narrow, 

 elongate spire. A. hypnorum is distributed in northern North America (La Rocque, 

 1968, p. 552, however, notes a record from Louisiana), northern Europe, and Asia 



In our collections, A. hypnorum occurs as a single, immature shell at the 

 8- to 10-foot level of locality 135-1 (fig. 3). It is assumed that the species is 

 not a part of the indigenous faunal assemblages. 



Family Carychiidae 



Genus Caryohium Muller 1774 



Species of Caryohium possess minute elongate spiral shells that bear a 

 superficial resemblance to shells of pupillid gastropods. The animals live in 

 damp situations, often very near water but never in it; they live as terrestrial 

 pulmonates. The validity of the several named "species" in North America has 

 been questioned with considerable reason; the problem has been ably discussed 

 by La Rocque (1970, p. 558). 



Caryohium exile Lea 1842 



Caryohium exile H. C. Lea 1842, Amer. Jour. Sci., 1st ser., v. 42, 

 p. 109, pi. 1, fig. 5. 



Caryohium exile Lea, Pilsbry 1948, Land Moll. N. America, v. 2, pt. 2, 

 p. 1058, figs. 561c, 566a. 



Since this gastropod is represented in the two bog collections by a single 

 shell (fig. 3) occurring in the base of locality 135-1, precise identification was 

 not possible, since shells must be dissected to demonstrate the character of the 

 plait that ascends the columella. In any case, the single example of Caryohium 

 cannot be viewed as significant in the total faunal complex. 



Suborder Stylommatophora 

 Family Endodontidae 



Genus Helioodisous Morse 1864 



Gastropods of this genus have small discoid shells with tightly wound 

 whorls; the shell may resemble a gyraulid. In fact, Thomas Say described the 

 first species that subsequently was recognized as a member of the genus 

 Helioodisous -, the shell that he observed was discovered in a dried-up pond near 

 what is now Council Bluffs, Iowa, and he described it as a species of Planorbis. 

 However, the striking parallel striations of H. parallelus are entirely different 

 from any of those seen among the planorbids. The species of Helioodisous in 

 North America are found primarily east of the Rockies, although there are ex- 

 ceptions to this generalization. 



