PLEISTOCENE FOSSILS 



133 



Gastrocopt a (fig. 401) resembles Pupill a but has a more strongly 

 reflected lip. From Vertigo it differs in that the last whorl is not 

 constricted. Most of the species have strong internal lamellae but they 

 are weak and inconspicuous in some of them. Several species have been 

 collected in the Pleistocene of Ohio. 



Vertig o (fig. 402) is the smallest (less than l/l 6 

 inch) of the barrel-shaped land shells. It is recognized 

 by its constricted body whorl, the lamellae, which are 

 strong in most species, and its small size. Several 

 species occur in our Pleistocene. 



Fig. 402 



Columell a is also very small (l/l6 inch high) and 

 almost cylindrical; it is recognized by its high spire, small 

 aperture, and the absence of internal lamellae. C. 

 edentula (fig. 403) is a common species in the Pleistocene 

 of Ohio. 



Fig. 403 



Retinella (fig. 404) has a low-spired shell; the 

 surface is shining, even in fossil specimens, and has very weak axial Fig. 404 



ridges. The umbilicus is narrow or moderately wide. 

 , v ,./® The lip is thin and sharp. Two or three species are common in our Pleisto- 



:;*T^S cene. 



Fig. 406 



Fig. 405 



Striatura (fig. 405) is small (1/8 inch or less) with a low spire; the 

 strong ornamentation of axial and spiral ridges, the simple lip, and the absence of internal 

 lamellae are characteristic. Three species are common in pond and lake 

 deposits. 



In Planogyra the shell is small, the spire low. It is distinguished 

 from Striatura by fhe strong axial ridges which are parallel to the growth 

 lines; in Striatura the axial ridges are oblique. P. asteriscu s (fig. 406) 

 is commonly found in pond and lake deposits. 



Punctum resembles Striatura but is even smaller (a little more than 

 1/16 inch wide); the aperture is simple, sharp. It is distinguished from 

 Striatura by the lack of spiral ridges; the axial ridges are strong and distinct. _P. p ygmaeum 

 (fig. 407) is the common species of our Pleistocene. 



Fig. 407 



Hawaiia is a little larger than Punctum which it closely resembles 

 It has microscopic vertical ridges, the aperture is nearly round, and 

 the umbilicus is wide. H. minuscula (fig. 408) is common in pond and 

 lake deposits. 



The shell of Strobilop s is small (1/8 inch wide, globular but with 

 a flattened base; its shape suggests a beehive. It has 

 strong vertical ridges; the several internal lamellae 

 are spiral, extend far back into the shell, and bear 

 microscopic spines. S. labyrinthic a (fig. 409) is the 

 common species. 



X5.8 



Fig. 410 



lamellae, 

 deposits. 



Fig. 408 



Fig. 409 



Euconulus resembles Strobilops but lacks internal 

 The surface has only faint axial ridges. E. fulvus (fig. 410) is common in lake 



