292 paludinidj:. 



All the shells figured are from western localities, excepting Fig. 

 554, which are from the Delaware and Susquehanna Rivers, and 

 Fig. 552, which is from Massachusetts.] 



Ocnus AiniVICOLA, Gould and Haldeman. 1841. 



Shell ovate-conic, thin ; spire acute, composed of a few rounded 

 whorls ; aperture small, oblique, rounded-ovate ; lips continuous, 

 simple ; operculum horny, spiral, with a few volutions. 



Animal having an elongated foot, rounded posteriorly, with each 

 anterior angle produced laterally ; head half the hreadth of the foot, 

 and protruding beyond it ; tentacula short, filiform, unequal ? the 

 eyes seated at the side of the external base ; oviparous. Inhabits 

 fresh water. 



That this group of small shells should be separated from Paludina 



and also from Cyclostoma, in which genus they were included by 



Cuvier, is clear from the structure of the operculum, but 



Fig. 557. . . ^ ; 



more especially from the structure and habits of the animal. 

 Among the differences the following are the most obvicus : in 

 this genus the head precedes the foot in progression ; in Pal- 

 lum^of vdina it is the contrary ; in this the tentacula are all the way 

 la. of a size, and without any enlargement for the reception of 

 Enlarged. ^|_^g cycs, iustcad of being tapering, with a niche for the 

 eyes ; they are also frequently, if not always, unequal in length ; 

 perhaps this is a sexual difference. The animal has the power of 

 rising and swimming in an inverted posture at the surface of the 

 Avater, which the true Paludina never does. So far as observation 

 has yet gone the Amnicola is oviparous, while the true Paludina is 

 ovo-viviparous. It is found crawling upon stones, sticks, and aquatic 

 plants, while Paludina remains upon the mud, and is usually ob- 

 served partly, or entirely, imbedded in it. On these grounds Mr. 

 Haldeman concurs with me in instituting the genus Amnicola. Its 

 position seems to be intermediate between Paludina and Melania. 



Amnicola pallida. 



Shell thin, conical, whorls four and a half, convex, suture distinct; umbilicus 

 narrow ; aperture ovate-orbicular, angular posteriorly. 



Amnicola pallida, Haldeman, Mon. part 4, pp. 3 and 4 of wrapper (1842) ; Men. 12, pi. 



1, fig. 7 (1844?). — W. G. BiNXEY, L. and Fr. W. Shells, ill. 83, fig. 16.5 (186.3). 

 Amnicola lustrica, Adams, Thompson's Vermont, 169, 152 (1842), teste Haldeman. 



