18 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 487 



In the bog sediments under study here, it is erratically distributed among 

 five faunal assemblages at the Strawn locality (135-1, 135-2), but is absent 

 from the Batavia assemblages, locality 136 (fig. 3). Even where it does occur 

 in these sediments, it is rarely represented by more than one or two shells. 



Genus Promenetus F. C. Baker 1935 



F. C. Baker erected the genus Promenetus (Nautilus, 49:48) using 

 Planorbis exaouous Say as the type; later (1945) he recognized five species and 

 several varieties of these — which, of course, he referred to as subspecies — by 

 the form in which the so-called varietal names were used. The shells of species 

 in this genus are lenticular, with rapidly increasing whorls, and often with a 

 carina te periphery. 



Promenetus exaouous (Say) 1821 



Planorbis exaouous Say 1821, Acad. Nat. Sci. Philadelphia Jour., v. 2, 

 p. 168. 



Promenetus exaouous (Say), F. C. Baker 1945, Molluscan Family Planor- 

 bidae, p. 182, pi. 41, figs. 1-10. 



P. exaouous is distributed in North America east of the Rockies from 

 Canada to the mountains of New Mexico; it is absent from the central and 

 southern High Plains except as a Pleistocene fossil. 



Promenetus umbilioatellus (Cockerell) 1887 



Planorbis umbilioatellus Cockerell 1887, Conchologist's Exchange, 

 v. 2, p. 68. 



Promenetus umbilioatellus (Cockerell), F. C. Baker 1945, Molluscan 

 Family Planorbidae, p. 182, pi. 43, figs. 1-12. 



P. umbilioatellus was for many years considered as belonging in the 

 genus Gyraulus , but anatomical studies demonstrated its relation to Promenetus. 

 This species is almost universally represented in the two bogs under study here, 

 being absent from only two faunal assemblages (fig. 3) . Never present in abun- 

 dant populations, P. umbilioatellus is, nevertheless, represented in at least 

 moderate numbers where it occurs. It is, obviously, an indigenous element of 

 the total faunal assemblages of the two bogs. 



P. umbilioatellus lives today in northern United States and southern 

 Canada, and in high elevations in the Rockies as far south as New Mexico. 



Family Ancylidae 



Genus Ferrissia Walker 1903 



Shells of the gastropods of the genus Ferrissia are patelliform, or 

 limpetlike; the animals creep about on leaves, stems of reeds and sedges, aban- 

 doned shells of unionids, old bottles, and other smooth surfaces in quiet waters. 

 The shells are extremely simple and do not always reflect complexities that may 

 be present in the organization of the animal itself. The genus is worldwide in 

 distribution, but lacking in many places, such as, for example, Europe and 

 Latin America. 



Ferrissia parallela (Haldeman) 1841 



Anoylus parallelus Haldeman 1841, Monograph Limniades N. Amer., 

 pt. 2, p. 3. 



