54 RESEARCHES UPON THE IIYDROBIIN^ 



Z. lapidum, H. & A. Adams, Gen. Rec. Moll., I, (1854) 321, pi. xxxiv, 

 fig. 1. — Paludestrina lapidum, D'Okb., V07. Am. Merid., Moll., p. 382, pi. 

 xlvii, fig. 10-12. Buenos Ayres. 



L. perlstomatns, Stm. — Paludestrina peristomata, D'Okb., loc. cit., p. 3S2, 

 pi. xlvii, fig. 4-9. Buenos Ayres. 



The lingual dentition of the South American species is un- 

 known, and must be ascertained befqre those species can be said 

 with certainty to belong to the genus Lithoghjphus. They re- 

 semble the tyi)e in the form of the shell 



FLLMIXICOLA, Stm. 

 Fluminicola, Stimpson, Am. Journ. of Conch., I, (1865) 52. 



Shell comparatively large, obliquely ovate, thick, smooth, im- 

 perforate ; spire moderate, obtuse. Aperture ovate ; inner lip 

 flattened, callous ; outer lip effuse ond projecting anteriorly, so 

 that the peritreme is not continuously in the same plane. Oper- 

 culum corneous. Tentacles tapering. Rostrum rather large. 

 Foot broad. Yerge large, compressed, with a broad semicircular 

 laminiform expansion or wing on its left side. 



Lingual dentition of the type : Rhachidian tooth more than 

 twice as broad as long. Outer lateral tooth with a smaller number 

 of denticles than the inner. Formulaof the denticles : 3^- 6- 10- 7. 



Ova-capsules large, circular, depressed, almost discoidal, each 

 containing a large number of eggs. 



Station, fresh water. 



Distribution, Oregon and California. 



Type F. Nuttalliana, Stm. — Pahidina Nuttdftiana, Lea, Tr. Am. Phil. 

 Soc. VI, (1839) 101, pi. xxiii, fig. 89. Oregon. 



To which we add the following :- 



F. virens, Stm. — Paludina virens, Lea, loc. cit., VI, (1839) 91. Oregon. 

 F. nuclea, Stm. — Paludina nucha, Lea, loc. cit., VI, (1839) 91. Oregon. 

 F. semirxdis, Stm. — Paludina semiualis, Hinds, Voy. Sulphur, Moll., p. 54, 

 pi. xvi, fig. 22. California. 



F. Hindsii, Stm. — Amnicola Ilindsii, Baikd. 



