126 



OHIO FOSSILS 



Fig. 364 



The shell in Obovaria (fig. 363) is small, almost round, 

 with solid teeth, both laterals and cardinals. The species are 

 easily recognized by the thick shell, which is thickest in the 

 region of the beak. 



In the family Sphaeriidae, there are cardinal teeth under 

 the beak and one set of laterals on each side of the hinge. Iden- 

 tification of the species is a job for a specialist. For descrip- 

 tions, see Baker (1928a). The genera may be distinguished by 

 the following characters. 



In Sphaerium (fig. 364) the beaks are almost central, not 

 inflated; the shell is regularly ovoid. Individuals of several species 

 are common in Ohio Pleistocene lake and river deposits. 



Musculium (fig. 365) is similar to Sphaerium ; in fact, some 

 specialists consider the two genera identical. Species of Musculium 

 can be recognized by the swollen beaks, which are separated from 

 the body of the shell by a distinct groove. A few 

 species have been recorded in lake and pond deposits; 

 where they occur, they are often very common. 



In Pisidium (fig. 366) the shell is small and the beaks are nearer one 

 end of the shell than the other. The valves are thick, so much so that some 

 specimens at first sight look like a garden pea. It is very abundant in lake 

 and river deposits. 



GASTROPODA . The Pleistocene gastropods of Ohio belong to several 

 families but the characteristics on which they are based are not available in 

 the fossil shells. They can be identified to genus by shell characters which 



Fig. 365 



Fig. 366 



have been used exclusively in this book. 



Both land and freshwater snails are found in our Pleistocene deposits. No general rules 

 can be given to distinguish freshwater snails from land snails and they occur together in lake 

 and river deposits, the freshwater snails preserved in their natural habitat, the land forms 

 washed into the lakes and rivers by rains and floods. The following key will identify the 

 commoner genera. In the text, the genera are grouped according to their habitat. 



Key to the Commoner Pleistocene Gastropods of Ohio 

 (see p. 4 for use of keys) 



1. a) Shell saucer-shaped, not coiled Ferrissia 



b) Shell coiled 2 



2. a) Shell coiled in one plane 3 



b) Shell not coiled in one plane 7 



3. a) With axial ornamentation only 4 



b) With both axial and spiral ornamentation Helicodiscus 



