360 MOLLUSCA. 



same way above the head by a great solution of continuity; the sexes 

 are separated; the penis of the male is large, fleshy, and reflected 

 into the pectoral cavity; the two tentacula are terminated by blunt 

 tubercles, and two other tubercles, placed on their external base, 

 support the eyes. 



The shell is a spiral oval, with complete whorls, transversely and 

 finely striated, and its aperture, in the adult, is surrounded with a 

 small ridge. It is closed by a small round operculum. Found in 

 woods, under moss, stones, 8cc. 



The most common is the Turbo elegans, List., 27, 25, about 

 six lines in length and of a greyish colour; found under all the 

 mosses(l). 



Valvata, Mull. 



The Valvatae inhabit fresh water; their shell is convoluted in 

 almost one plane like that of a Planorbis, but the aperture is round, 

 and furnished with an operculum; the animal, which has two slen- 

 der tentacula, with the eyes at their anterior base, respires by means 

 of branchiae. In a species found in France, 



Valv. cristata, Mull.; Drap., I, 32, 33; Gruet-Huysen, Nov. 

 Act. Nat. Cur. X, pi. xxxviii, the branchiae, formed like a 

 feather, project from under the mantle and float externally, 

 vibrating with the breathing of the animal. On the right side 

 of the body is a filament which resembles a third tentaculum. 

 The foot is divided, anteriorly, into two hooked lobes. The 

 penis of the male is slender, and reflected into the branchial 

 cavity. The shell, which is hardly three lines broad, is greyish, 

 flat, and umbilicated. Found in stagnant water(2). 



It is here that we must place the completely aquatic shells, 

 or those respiring by branchiacj which belonged to the old 

 genus Helix ; i. e., those in which the penultimate whorl 

 forms, as in the Helices, Lymnaese, &c., a depression which 

 gives the aperture more or less of the figure of a crescent(3). 



The three first genera are still closely allied to Turbo. 



(1) Add Turbo lincina, List., 26, 24;— T. labeo, List. 25, 23;— T. duhms, IJorn., 

 XIII, 5, 6;—T. liinhatus, Chemn., IX, cxsiii, 1075. 



We should distinguish, among- the fossils, the Cyclostoma mumia of Lam., 

 Brongn., Ann. du Mus., XV, xxii, 1. 



(2) Add, Valvata planorbis, Drap., I, 34,35; — V. mmuta,ld., 36 — 38. 



(3) They constitute the Ellipsostoma of M. de Blainville. 



