130 



OHIO FOSSILS 



Fig. 373 



Fig. 375 



The shell of Lymnaea is large, up to 2. 5 inches long, thin, with a 

 sharply pointed spire and a large aperture. The inner edge of the aperture 

 is widely reflected over the umbilicus which it closes almost entirely. 

 L. stagnalis (fig. 373) is common in lake deposits. 



Bulimnea has almost as large a shell as Lymnaea 

 but its spire is shorter and stouter, with more swollen 

 whorls. The color of the fresh shell is purplish brown 

 and some of the color is preserved in fossil shells. B. 

 megasoma (fig. 374) is common in some lake deposits. 



In Stagnicola (fig. 375) the shell is of much the 

 same shape as in Bulimnea but with a longer spire and 

 smaller aperture. Shells of this genus are smaller than the 

 preceding two genera, seldom attaining more than 1. 5 inches. 

 Several species are common in lake and river deposits in our 

 Pleistocene. 



Pseudosuccinea has a shell of medium size, 5/8 to 3/4 inch 

 long; the aperture is longer than the spire, wide and flaring; the 

 surface has minute spiral and vertical ridges, a feature which dis- 

 tinguishes Pseudosuccine a from Succinea and Qxyloma which have 

 only axial ridges. P. columella (fig. 376) is common in small-lake 

 deposits in Ohio. 



Fig. 374 



Fig. 376 



Fossaria (fig. 377) has a shell much like that of the preceding two genera but 

 much smaller. The differences between the three genera are anatomical and it is 

 not always possible to distinguish Fossaria from them. A shell having this general 

 aspect and less than 1/2 inch long can be safely referred to Fossaria . Several 

 species of the genus are common in all freshwater beds. 



Shells of the following four genera are commonly called "ramshorn snails" 

 because of their shape. Those of the genus Helisoma are the largest of the group. 

 Flg ' The three commoner species may be separated by means of the following key: 



a) Spire sunken, in the shape of a funnel; umbilicus 



deep H. anceps (fig. 378) 



b) Spire flat, sometimes rising a little above 



the body whorl; umbilicus deep; 



aperture bell-shaped H. campanulatum (fig. 379) 



c) Spire flat, almost always lower than the 



body whorl, aperture not bell- 

 shaped H. trivolvis (fig. 380) 



These three species are common in both river and lake deposits in Ohio. 



Fig. 378 



Fig. 379 



Fig. 380 



