no MOLLUSC A FROM THE CRAG. 



Paludina,* Lamarck. 

 Helix (spec.) Linn. 



Gen. Char. Shell ovato-conical, or subglobulous, and in the recent state thin, 

 corneous, or semitransparent spire, more or less elevated, with rounded or convex 

 volutions; aperture subcircular or ovate, slightly impressed by the previous whorl, and 

 somewhat angulated at the upper part ; operculum corneous or calcareous, formed of 

 concentric laminae. 



Shells belonging to this genus in the recent state are found in water that is quite 

 fi'esh, and the habits of the animal are much like those of Lymnsese, although it is 

 said to be furnished with pectinated branchiae. 



This genus first appears in the Wealden formation, in what is considered by 

 Dr. Mantell to be a fi-esh-water deposit, or probably the embouchure of an enormous 

 river. In the Eocene formations of this country at Hordwell, a species of this genus is 

 found associated with what may be considered as purely fresh-water animals, while the 

 species found in the Mammaliferous Crag are mixed with decidedly marine species. 



L Paludina lenta. Brander. Tab. XII, fig. 1, a — c. 

 Helix lenta. Brand. Foss. Hanton. fig. 60, 1766. 

 ViviPAEA LENTA. J. Soiv. Min. Conch, t. 31, fig. 3, 1813. 



— CONCINNA. - - - t. 31, fig. 4-5. 

 Cyclostoma unicolor. Oliv. Voy. pi. 31, f. 9 a, b. 



Paludina lenta. Besh. Coq. foss. des Env. de Paris, p. 128, pi. 15, fig. 5-6, 1825. 



— semicaeinata. - - - p. 127, pi. 15, fig. 11-12. 



— MEDIA. Woodward. Geol. of Norf. t. 3, fig. 5-6. 



— EOTtlNDATA. - - - t. 3, fig. 7, 1833. 



— OBSOLETA. - - - t. 3, fig. 4. 



— UNicoLOB,, Lam. Hist, des An. sans Vert. 2d edit. torn, viii, p. 513, 1838. 



— — S. Wood. Catalogue 1842. 



— — CaiUiaud. Voy. a Meroe, pi. 60, fig. 7. 



— — Saviyny. Egypt, pi. 2, fig. 30. 



B. Testa ovatd, conoided, crassd ; apice acuta ; sj)ird elevatd ; anfractibus quinque, rotun- 

 datis, IcBvigatis ; aperturd obovatd, superne acuminata, peristomate integro ; umhilico ohtecto. 



Shell ovato-conical, with an elevated spire and acute apex ; volutions convex and 

 smooth, with occasionally a few obsolete striae ; aperture subcircular, slightly acuminated 

 at the upper part ; margin continuous, and umbilicus closed. 



Axis, 1 inch. 



Locality. Mam. Crag, Bramerton and Thorpe. Recent, Nile River. 



This shell is by no means rare at the above localities, and much too numerous to 

 be considered as casually introduced, like Planorbes, Lymnma, and the Helices. The 

 specimens are variable in form, as may be seen in the figures referred to in our own 

 plate, and I have no doubt the shells figured by Woodward belong to one and the 



* Palus-udis, a marsh or lake ; the general place of habitation for these animals. 



