450 FRANK COLLINS BAKER 



Planorhis exacuous Say. This flat, lens-shaped Planorhis is 

 fairly common in this deposit. The specimens are of large size, 

 several individuals measuring 6 mm. in greatest diameter. 



Lymnaeidae 



Galha palustris (Miiller). A single broken specimen of a lym- 

 naeid is referable to this protean species. When perfect it must 

 have measured nearly 40 mm. in length. 



Galha ohrussa decampi (Streng). This small lymnaeid is quite 

 common in the deposit. It exhibits more or less variation, prin- 

 cipally in the degree of elevation of the spire, in the convexity of 

 the whorls, and in the shoulder of the whorls. This species is 

 characteristic of the cold waters of the early Wisconsin ice recession, 

 in which it lived in considerable abundance. It is apparently 

 much less common living in the recent fauna than it was in post- 

 glacial or interglacial times. 



Physidae 



Physa anatina Lea. This la,i ge Fhysa is apparently a form of 

 Lea's species, which occurs abundantly in the states west of the 

 Mississippi River. It is recorded from Michigan and is said to 

 range clear across the southern part of this state (see Walker). 

 It is also recorded from Hardin, McHenry, and Adams counties, 

 Illinois (see Baker, III. Cat.). There seems to be no reason why it 

 should not be found as far east as Ohio. 



The Ohio shells differ from typical anatina in being larger, with 

 a wider body whorl and aperture and more flat-sided spire whorls. 

 Adult individuals are not common in the deposit, but immature 

 shells of four whorls are almost abundant. Variation is so great in 

 this genus that it has not been thought best to bestow a name on 

 this form, although it differs more or less widely from the average 

 recent shells of anatina. 



Ancylidae 

 Ferrissia parallela (Haldeman) . A single specimen of this 

 fresh-water limpet was found in the material examined. As about 

 20,000 shells were picked over it must be considered very rare. 

 The specimen is typical. 



