52 MOLLUSCA. THACHELIPODA. 



N. elliplica, Lam. Shell ovate, elliptic, under a fuscous green epi- 

 dermis, smooth, shining, with white and bluish spots ; apex re- 

 curved, prominent, beyond the margin. 13 lines long. Inhabits 

 rivers in the Isle of France Ckem. ix. pi. 124, fig. 1082. 



FAMILY VII. PERISTOMIDA. 



Shell operculated, conoid or subdiscoid, with the margin of the 

 aperture united ; fluviatile, and the animal respiring in water. 



Gen. 59. AMPULLARIA, Lam. Helix, Lin. Nerita, Muller. 

 Shell globular, ventricose, the base umbilicated ; inner lip not 



callous; aperture entire, oblong, with the margin united; outer 



margin acute, not reflected. 



This genus is composed of shells found in the rivers of warm countries. The co- 

 lumellar margin is reflected over the umbilicus, without producing any callosity. 

 The shells in general are of pretty large size. 



A. Guyanensis, Lam. Shell ventricose, globose, solid, longitudi- 

 nally and unequally striated ; epidermis fuscous ; six whorls, the 

 last longest ; aperture golden. 3 inches in diameter. Inhabits 

 rivers of Guiana. Lister, pi. 128, fig. 28. 



A. rugosa, Lam. Shell ventricose, globose, solid, rugous, yellowish 

 white, epidermis chestnut, with unequal longitudinal wrinkles ; 

 whorls six, the last longest ; aperture milky. 3 inches in dia- 

 meter. Inhabits the river Mississippi. Lister, pi. 125, fig. 25. 

 Fossil shells of this genus have been found on the Continent at Grignon, An. 



Mus. v. 30. 



Gen. 60. PALUDINA, Lam. Helix, Lin. 

 Shell conoid, with the whorls rounded or convex ; aperture 

 rounded, ovate, longer than broad, and angular at the sum- 

 mit ; margins united, edged, never reflected ; an orbicular 

 horny operculum. 



The shells of this genus generally inhabit fresh waters, though some are found 

 in salt marshes. The animal has two linear subulate tentacula, with eyes at the 

 base ; the mouth triangular ; the foot subtriangular ; and the branchiae composed of 

 tufted filaments. 



P. vivipara, Lam. Shell diaphanous, ovate, ventricose, obtuse, and 

 longitudinally wrinkled ; aperture suborbicular, and the pillar 

 lip slightly reflected ; colour olive, with three brown bands on the 

 body whorl. 1| inch long. Inhabits fresh waters in Europe. B. 

 Brown's Illust. pi. 42, fig. 68, 69. 



P. impura, Lam. (H. tentaculata, Lin.) Shell ovate, conoid, smooth, 

 pellucid, shining horn colour, with five whorls, the last ventri- 

 cose ; spire acute. 5 lines long. Inhabits rivers in Europe. B. 

 Brown's Illust. pi. 42, fig. 72, 73. 



Gen. 61. VALVATA, Lam. Helix, Gmel. 

 Shell discoid or conoid, with cylindrical whorls ; aperture round- 

 ed, with the margins united and edged ; operculum orbicular. 



V. piscinalis, Lam. (Nerita, Muller.) Shell globose, conoidal, sub- 



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