292 PALUDINID^. 



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.] 



Genus AMNICOL..4, 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 havhig an elongated foot, rounded posteriorly, with each 

 anterior angle produced laterally ; head half the 1)readth 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 Paliidina 



and also from Ci/clostoma, in which genus they were included by 



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



Fis 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- 

 ndhia it is the contrary ; in this the tentacula are all the way 

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

 Enlarged, ^j^^ ^^^^^^ iustcad of bciug taijcring, 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 

 water, which the true Paludina never docs. 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 acjuatic 

 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 Mclania. 



Amnicola pallida. 



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

 narrow ; aperture ovate-orbicular, angular posteriorly. 



Amnicola pallida, Haldemav, 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. 165 (186:)). 

 Amnicola lustrica, Adams, Thompson's Vcrmontj 169, 152 (1842), teste Haldkman. 



