90 Trans. Acad. Sci. of St. Louis. 



113. Planorbis bicarinatus Say. 



Stations 5, 6, 9 and 17. Rochester (Walton). Very 

 common everywhere and also subject to great deformity. 



Subgenus Gyraulus Agassiz. 



114. Planorbis deflectus Say. 



Stations 5, 6 and 11. Brighton (Walton). Common and 

 typical. 



*115. Planorbis hirsutus Gould. 



Mr. Walton reports rinding this species in the Erie Canal. 



116. Planorbis parvus Say. 



Stations 5 and 6. Charlotte (Walton). Very common 

 everywhere. Found in 8pirogyra. 



Genus Segmentina Fleming. 

 Subgenus Planorbula Hald. 



117. Segmentina armigera Say. 

 Station 5. Brighton (Walton). 



Subfamily Ancylinae. 

 Genus Ancylus Geoffroy. 

 *118. Ancylus parallelus Haldeman. Charlotte. 

 *119. Ancylus tardus Say. Irondequoit. 

 *120. Ancylus rivularis Say. Genesee River. 



Family Physidae. 



Genus Physa Drap. 



121. Physa heterostropha Say. 



Stations 3, 4, 5, 6, 8, 9, 10 and 11. Common everywhere 

 and exceedingly variable. 



A recent study of this genus convinces the writer that of 

 the seventy odd species described at the present time, there 

 are really but ten or a dozen valid names. The following 



