156 AMERICAN JOURNAL 



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Hydrobiin^e. Shell elongated, perforate, smooth. Opercu- 

 lum corneous. European and American. Littorinella, 

 Hydrobia, Bythinella, Paludestrina* 



Amnicolin^e. Shell turbinate ; whorls very convex, umbili- 

 cate ; aperture round ; peristome continuous. Ameri- 

 can. Amnicola. 



Pomatiopsin^e. Foot with lateral sinuses. Shell elongate ; 

 margin of aperture slightly expanded. Terrestrial or 

 amphibious. American. Pomatiopsis. 



CochliopiNjE. Shell heliciniform, heavy; aperture oblique ; 

 umbilicus large, with an angulated margin. American. 

 Cochliopa.f 



Lithoglyphin^e. Shell subglobular ; spire short ; aperture 

 large, half round; peristome not continuous; imperforate 

 or slightly perforate. European and American. Qillia, 

 Somatogyrus, Lithoglyphus, Fluminicola. 



For comparison, we copy the arrangement of Hydrobiinse 

 adopted by Dr. Stimpson. 



* The animals of Tricula, Pyrgula, and Tryonia are undescribed, and I 

 will not venture to assign their place, believing that the two last named 

 belong decidedly to another family. Does not Potamopyrgus, St., belong 

 to the same group ? 



t I almost doubt the pertinence of CocMiopa to this family, although Dr. 

 Stimpson's description of the Soft Parts seems to place it here. 



