m 



Paludina, Lam. 



This genus has lately been separated from the Cyclostomse, because 

 there is no ridge round the apertiu'e of the shell ; because there is a 

 small angle to that aperture as \\'ell as to the operculum, and finally, 

 because the animal, being provided with branchiae, inhabits the 

 water, like all other genera of this famil5^ It has a very short snout 

 and two pointed tcntacula; eyes at the external base of the latter, but 

 on no particidar pedicle, and a small membranous wing on each side 

 of the fore part of the body. The anterior edge of the foot is double, 

 and the wing of the right side forms a little canal which introduces 

 water into the respiratory cavity, the incipient indication of the siphon 

 in the following family. 



The common species. Helix vivipara, L. ; Drap., I, 16, whose 

 smooth and greenish shell is marked with two or three purple, 

 longitudinal b.mds, and which abounds in stagnant waters, in 

 France, produces living young ones : in the spring of the year 

 they may be found in the oviduct of the female, in eveiy stage 

 of develo])ment. Spallanzani assures us that if the young ones 

 be tak(>n at the moment of birth and be reared separately, they 

 will reproduce without fecundation, like those of the Aphis. 

 The males, however, are nearly as common as the females ; they 

 have a large penis which protrudes and retracts, as in Helix, 

 but through a hole pierced in the right tentaculum, a circum- 

 stance wliich renders that tentaculum apparently larger than 

 the other, and which furnishes us with a mode of recognizing 

 the male *. 



The Ocean produces sonic shells which only differ from the Palu- 

 dinse in being thick. They form the 



LiTTORiNA, Feruss., 



Of whicli the common species, Le Vigneau — Turbo /ittoreus, L., 

 Chemn. V, clxxxv, 1852, abounds on the coast of France, where it is 

 eaten. The shell is round, brown, and longitudinally streaked Avitli 

 blackish. The 



MoxoDox, La?u. 



Only differs from Littorina in having a blunt and slightly salient 

 tooth at the base of the coliunella, which sometimes has also a fine 

 notch. The external edge of the aperture is crenulated in several 

 species. The animal is more highly ornamented, and is generally 

 furnished with three or four filaments, on each side, as long as its 

 tentacula. The eyes are planted on particular pedicles at the exter- 

 nal base of the tentacula ; the opercukun is round and horny. 



♦Add, Cyclost. achalinum, Drap. I, 18; — C. impurum, Id., 19, 20, or Helix 

 tentaculata, L,, &c. ; and the small species of salt-water ponds described by Beu- 

 dant, Ann. du Mus., XV, p. 199. 



