OF CONCHOLOGY. 53 



armed Avitli six denticles at tlie summit ; inner lateral with 

 ten, outer lateral Avitli seven. 



Ova deposited in circular groups, enclosed in a common, 

 corneous envelope or capsule. 



Station, — Fresh water. 



Distribution. — Oregon and California. 



Type, F. nuttalliana. 

 Paludinanidtalliana Lea. — Trans. Amer. Philos. Soc, vi., 

 1839, p. 101, pi. xxiii., f. 89. 



The Pahidina v.'rens Lea, P. nuclei Lea, P. seminalis Hinds, 

 and Amnicola Hindsii Baird, will fall into the same genus. 



GILLIA. 



Shell rather large, subglobular, thin, subperforate, smooth ; 

 spire small ; suture not impressed ; aperture large, broad, 

 ovate, oblique, with the outer W^) thin, acute, and not pro- 

 jecting anteriorly. 



Operculum subspiral, thin, corneous, regularly ovate. 



Foot oblong, broadly rounded behind, and strongly auricu- 

 lated in front. Rostram rather large. Tentacles tapering, 

 pointed. Verge small, simple, lunate. 



Lingual dentition of type :■ — -Rhachidian tooth deeply trilo- 

 bate below, with the onter angles much produced; cusp with 

 nine denticles ; basal denticles two on each side, rather close 

 to the basal margin, and projecting beyond it. Intermediate 

 tooth with the body subrhomboidal, slightly excavated at the 

 middle, and the peduncle as long as the body, but only half 

 as broad. Liner lateral tooth with fourteen denticles ; outer 

 lateral with ten. , 



Ovacapsales hemispherical, each containing but one Qg^, 

 and deposited singly or in groups, or linear series. 



Station. — Fresh water. 



Distribution. — North America^ east of the Alleghanies, from 

 Pennsylvania to Georgia. 



Type, G. alttlis. 



Melania aUilis Lea, Trans. Amer. Philos. Soc, viil., 1843, p. 

 174, pi. v., f. 23. 



POTAMOPYRGUS. 



Shell ovate-conic, imperforate ; apex acute ; whorls coronated 

 with spines ; outer whorl nearly two-thirds the length of the 

 shell ; aperture ovate, outer lip acute. 



Operculum corneous, subspiral. 



Foot rather short for the length of the shell, broadest in 

 front and strongly auriculated. Tentacles very long, slender, 

 and tapering. Eyes on very prominent tubercles. . Rostrum 

 of moderate size. 



