24 RESEARCHES UPON THE HYDROBIINiB 



Genus FLIHWIXICOLA, Stm. 



In the "Transactions of the American Philosophical Society," 



Yol. YI, 1839, p. 101, pi. xxiii, fig. 89, Dr. Lea has described and 



figured a shell (Fig. 15, enlarged) from the Columbia River, 



Oregon, under the name of Paludina Nuttalliana. 



^^' ' Subsequently, in a " Report on the Survey of the 



Northern Pacific Railroad Route," Mr. William 



Cooper placed this species in Amnicola, having 



probably observed that its operculum is subspiral, 



and not concentric as in Paludina. Mr. Binney 



having kindly sent me specimens of this mollusk 



preserved in spirits, I have examined its characters, 



which prove it to be distinct from Amnicola proper, although 



Mr. Cooper, in placing it in that genus, has made a much closer 



approximation to the truth than did its original describer. 



The shell is larger than in any of the other genera of Hydro- 

 biinse, and resembles in size and general appearance that of the 

 ieptoa:zs-group of Melanians. It is also so like that of the 

 Paludina decisa and its allies, that it is by no means surprising 

 that it should have been referred to their vicinity by the dis- 

 tinguished naturalist who first described it, as the operculum 

 was then unknown. In fact we find it to have the same shape, 

 the same eroded apex and olive periostraca, and the same form 

 of aperture with prominent outer lip and sinuated base, which 

 are characteristic of the Eastern Melanthos (Campelomse). 

 These characters of the shell and its aperture will serve to dis- 

 tinguish the new genus Fluminicola, which has the species under 

 consideration for its type, from all other Hydrobiinae. The soft 

 parts also furnish good distinctive marks. 



The shell (Fig. 15) may be described as follows : — It is rather 

 thick and strong, subglol)ular or subovate inclining to conic, im- 

 perforate, and simply striate. Periostraca thick, greenish-olive. 

 Spire obtuse. Suture scarcely impressed. Aperture ovate, 

 rounded in front, angular beliind ; columella concave, flattened, 

 and callous, especially near the umbilical region ; margin of the 

 peritreme not in the same plane, but sinuated. 



Having only alcoholic specimens of the animal for examina- 



