PLEISTOCENE FOSSILS 



129 



41. a) Adult more than 1/2 inch wide Mesodon and related genera 



b) Adult less than 1/2 inch wide 42 



42. a) Shell globular 43 



b) Shell like a thick lens 44 



43. a) With internal lamellae Strobilops 



b) Without internal lamellae Euconulus 



44. a) Shell only a little wider than high Vallonia 



b) Shell much wider than high Planogyra 



a) Freshwater Genera 



In Campeloma (fig. 367) the shell is large (1. 25 to 1.5 inches or more long) 

 spire often eroded. The aperture is rounded and not reflected over the 

 umbilicus. This group of snails lives in shallow, quiet water, on mud and 

 sand. Several species live in Ohio; a few have been found as fossils. 



The shell in the genus Valvata is small; the umbilicus is large and 

 deep; in one Ohio species, V. tricarinata (fig. 368) the shell has three 



keels, one on the shoulder of the whorl, one in 

 the middle, and one at the base. In two other Ohio 

 species, V. lewisi and V. sincera, there are no 



tricarinata. 



green, the 



keels but the shape is the same as in V. 



V. lewisi has a wide umbilicus and low spire; V. 



sincer a has a narrow umbilicus and high spire. 



Fig. 367 



Fig. 368 



Amnicola (fig. 369) has a small shell (1/8 to 1/4 inch 

 high), the spire is moderately high, the umbilicus narrow, the aperture entire and 

 not reflected over the umbilicus. Several species have been recorded from the 

 Pleistocene of Ohio. 



Fig. 369 



Fig. 370 



Cincinnatia (fig. 370) is similar to Amnicola , but with the first 2 whorls 

 coiled in the same plane; it is about the same size as Amnicol a. A few species 

 are abundant in our Pleistocene. 



Goniobasis (fig. 371) is the commoner of two very long -spired 

 genera; it is of medium size, 1 to 1. 5 inches long, and is distinguished 

 from Pleurocera by its rounded lip which is not prolonged into a short 

 canal below. Species of this genus are particularly abundant in river 

 deposits. 



Fig. 371 



Pleurocera (fig. 372) is similar to Goniobasis but has an even higher spire. 

 The lower lip is prolonged into a short canal and the shell seems therefore to be 

 slightly pointed below. It is also found in river deposits, but not as commonly as 

 Goniobasis. 



Fig. 372 



