GASTEKROPODA. HELICID. 85 
it Clausilia, from its internal operculum, a character not yet 
observed in any other genus. About forty species are known, 
four of which are natives of Britain. 
The operculum affords some characters to assist in specific 
distinctions. Its posterior spiral extremity is rather abruptly 
notched near its apex on one side, and is then gradually acu- 
minated in all the indigenous species. 
1. CLAUSILIA LAMELLATA. 
C. testa subventricosa, cornea, levi, nitida, pellucida; aper- 
tura bilamellata. 
Helix bidens, Mill. Verm. Hist. 315. 
Bulimus bidens, Brug. Encycl. Méth. xvi. Vers. 352. 
Turbo laminatus, Mont. Test. Brit. 359. t. 11. fig.4; M. & 
R. Trans. Linn. Soc. vin. 179 ; Dill. Dese. Cat. 874; Turt: 
Conch. Dict. 224. 
Clausilia bidens, Drap. Hist. des Moll. 68. 
Odostomia laminata, Flem. Edinb. Encycl. vii. 76. 
(3. albida. 
Animal cinereum. Latera grisea, albido-sparsa. Dorsum in- 
terdum nigrescens. Operculum prope apicem anticum ad 
sinistram emarginatum ; apice ipso truncato, emarginato : 
laciniis rotundatis. 
Habitat in sylvis, seepius sub muscis ; / in cretaceis. 
Shell somewhat ventricose, horny, surface as if smooth, 
shining and pellucid ; aperture with two white lamellee. _Peri- 
treme white. Height three-quarters of an inch. 
Although this species appears at first sight to be perfectly 
smooth, yet, on examination, the whorls will be found to be 
faintly striated transversely. In fine specimens these strize 
may always be distinctly seen on the last whorl, and on the 
right side of all the other whorls. 
Inhabits woods, and is generally to be found beneath moss. 
In wet weather it frequently ascends the trunks of trees. The 
white variety was communicated to me by my kind friend, 
J. F. Stephens, Esq. who found it in the chalky districts around 
Darent, in Kent, where it is occasionally found. 
