132 



OHIO FOSSILS 



Mesomphix (fig. 391) is similar to Haplotrema out has whorls that 

 increase rapidly in size; the shell is very thin and fragile and therefore 

 is often represented only by fragments in our lake deposits. Two or 

 three species are common in the Pleistocene of Ohio. 



Vitrina has a shell of only 3 whorls, enlarging rapidly, the last whorl 

 much larger than the other two; the shell is thin, the aperture simple, the 

 lip sharp. V. limpida (fig. 392) is the common species in the Pleistocene 

 of Ohio. 



Fig. 392 



Fig. 393 



In Zonitoides (fig. 393) the shell is small or of medium size, with a slightly 

 elevated spire. The umbilicus is moderately wide, the lip simple, sharp. 

 Ornamentation of faint, crowded axial striae only. Two species are common in 

 our Pleistocene. 



Discus is similar to Zonitoides but has a much wider umbilicus. 

 The ornamentation is of coarse, widely spaced axial striae. The 

 shoulder is angulated to rounded. Discus cronkhitei (fig. 394) is 

 common in the Ohio Pleistocene. 



In Vallonia (fig. 395) the shell is small, a little wider than high; the 

 most conspicuous feature is the reflected lip which is of the same width 

 all round. Common in lake deposits. 



Fig. 394 



Helicodiscus is so like the smaller ramshorn shells 



Fig. 395 



Fig. 396 



Fig. 397 



Fig. 399 



that it was first described under the genus Planorbis , by mistake. It is now 

 known to be a land snail. The shell is small (1/8 inch wide), the spire very low. 

 The surface has both axial and spiral ridges. Helicodiscus parallelus (fig. 396) 

 is common in pond and lake deposits. 



Zo'ogenetes is also small (3/16 inch high) but the spire is higher than that of 

 Helicodiscu s. The surface has strong axial ridges; the aperture is oval, the lip 

 sharp. Z. h arpa (fig. 397) is common in some pond deposits in Ohio. 



In Cionell a the shell is longer than wide, small (1/4 inch high), 

 very smooth and shining, the aperture narrowed below. It has no 

 internal lamellae. C. lubrica (fig. 398) is common in pond and small 

 lake deposits in Ohio. 



Carychium (fig. 399) resembles Cionella but is much smaller 

 (about 1/16 inch long) and it has a reflected lip and elongated 

 aperture. There is one internal lamella. The surface bears 

 weak axial ridges. Two or more species are represented in the 

 Pleistocene of Ohio. 



Fig. 398 



Pupilla is one of 4 genera with a barrel-shaped shell. It is small 

 (length 3/8 inch), the aperture is thickened and bears one or two lamellae or 

 none at all. The lip is less reflected than that of Gastrocopt a and the last 

 whorl is not constricted as in Vertigo . Pupilla muscorum (fig. 400) is 

 abundant in some pond beds in Ohio. 



