GASTEROPODA PECTINIBRANCHIATA. 361 



Paludina, Lam. 



This genus has lately been separated from the Cyclostomse, because 

 there is no ridge round the aperture of the shellj because there is a 

 a small angle to that aperture as well as to the operculum, and finally, 

 because the animal, being provided with branchiae, inhabits the 

 water, like all other genera of this family. It has a very short snout 

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

 on no particular 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 si- 

 phon in the following family. 



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

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

 longitudinal bands, 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 every stage 

 of development. Spallanzani assures us that if the young ones 

 be taken 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 which renders that tentaculum apparently larger than 

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

 the male(l). 

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

 dinse in being thick. They form the 



LiTTORiNA, Feruss., 



Of which the common species, Le Vigneau — Turbo littoreus^ L. , 

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

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

 Avith blackish. The 



MoNODON, Lam. 



Only differs from Littorina in having a blunt and slightly salient tooth 

 at the base of the columella, Avhich sometimes has also a fine notch. 



(1) Add: Cyclost. achatinum, 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. 

 Vol. 11.-2 V 



