gasteropoda pectinibranchiata . 
57 
Cyclostoma, Lam.* * * § ^ 
The Cyclostomae sliould be distinjOfuishcd from all the others be- 
cause they are terrestrial, as instead of branchiee, the animal has 
merely a vascular network spread over the parietes of its pectoral 
cavity. In eveiy other respect, however, it resembles the other 
animals of this family; the resjnratory aperture is formed in the 
same way above the head by a great solution of continuity; the 
sexes are separated; the penis of the male is large, fleshy, and re- 
flected into the pectoral cavity ; the tv.'o tentacida are terminated by 
blunt tubercles, and two other tubercles, placed on their external 
base, sujjport 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, &c. 
The most common is the Turbo elegans. List., 27, 25, about 
six lines in length and of a greyish colour; found under all the 
mossesf. 
Valvata, Mull. 
The ValvattC inhabit fresh water ; their shell is convoluted in 
almost one plane like that of a Planorlds, but tlie aperture is I’ound, 
and furnished with an operculum; tlie animal, which has two slen- 
der tentacula, with the eyes at their anterior base, respires by means 
of branchiee. In a sjjecies found in France, 
Frt/y. Mull.; Drap., I. 32,33; Gruet-Hu 5 '’scn, Nov. 
Act. Nat. Cur. X, pi. xxxviii, the branchia', formed like a 
feather, project from under the mantle and float externally, vi- 
brating with the breathing of the animal. On the right side of 
the l)ody 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 cavit}'’. 
Tlie shell, winch is hardly three lines broad, is greyish, flat, 
and umbilicated. Found in stagnant watcr|. 
It is here that we must place the completely aquatic shells, or 
those respiring by branchia;, which belonged to the old genus Heeix; 
i. e., those in wliich the penultimate Avhorl forms, as in the Helices, 
Lymnscae, &c,, a dejiression which gives the aperture more or less of 
the figure of a crescent §. 
The three first genera arc still closely allied to Turbo. 
* The CijdosfoiiKC .mil the tlelicuies form the order of the Pulmonka Opercu- 
LATA of M. dc Feru'^sae. 
t Add, Turbo liucina, List., 26, 24 ; — T. labeo, List., 25, 2.3; — T. iJuhius, Born., 
XIII, 5, 6 ; — T. liinbaUtif, Chemn., IX, cxxiii, 1075. 
We should distinguish, among the fossils, the Ci/cluxfonia mumia of Lam., Brongn., 
Ann. du !Mus., XV, xxii, 1. 
J Add, Valuata plaiwrhis, Drap., I, 34, 35 ; — V. inimita. Id., 36 — 3S. 
§ They constitute the Ellii'sostoma of liL de Blainville. 
