12 THE MOLLUSC A OF MUSCATINE COUNTY. 



whirls ; is perfect to the apex. Length of shell, 51 ; of aper- 

 ture, 23 mm. 



M. decisa, SAY. Abundant. I doubt very much if any well- 

 marked difference exists between this and the preceding. 

 Length of shell, 34 ; of aperture, 18 mm. A reversed " dead " 

 shell, probably a decisa, was found at Moscow in this county. 

 We have examples of this genus from Alabama, New York, 

 Ohio, Michigan, Illinois, and Iowa : they are called ponderosa, 

 obesa, Integra, decisa, subsolida, rufa, etc. In the whole 

 range there seems to be no more difference or variation than 

 exists in our H. multilineata. The larger and heavier shells 

 are in our streams ; the lighter, in our ponds. 



LIOPLAX. 



L. subcarinata, SAY. Common. In ponds. Most specimens 

 show a carina near the apex. Length of shell, 16 ; of aper- 

 ture, 8 mm. 



BSSOi 



BYTHINELLA. 

 B. obtusa, LEA. Rare. In ponds. Length, 4.2 mm. 



SOMATOGYRUS. 



S. isogonus, SAY. Common. In ponds and slow-running streams. 

 Length of shell, 8.2 ; of aperture, 5.8 mm. 



AMNICOLA. 

 A, cincinnatiensis, ANTHONY. Common. Ponds. Length, 5 mm. 



POMATIOPSIS. 



P. lapidaria, SAY. Ver}^ rare. We have in our collection three 

 good specimens of "dead" shells, evidently of this species, 

 which we found among drift-wood on the bank of the Missis- 

 sippi, about two miles above Muscatine. They could hardly 

 have come from the loess, a mile or two farther up, since we 

 have not yet found them in this deposit anywhere in this 

 region ; and we have not found other shells of the loess along 

 the river in this way. Length of shell, G.8 ; of aperture, 

 2.2 mm. 



