GASTEROPODA PUEMONEA. 
37 
PULMONEA AQUATICA, 
Have only two tentacula, as already stated ; they are continually 
compelled to rise to the surface for the purpose of breathing, so 
that they cannot inhabit very deep water; they are usually found 
in fresh water or salt ponds, or at least in the vicinity of the sea- 
coast and of the mouths of rivers. Some of them have no shell, 
such as 
Onchidium, Buchav*. 
A broad, fleshy mantle, in the form of a shield, overlapping the foot 
at all points, and even covering the head when it contracts. It has 
two long retractile tentacula, and on the mouth an emarginated veil, 
formed of tAvo triangular and depressed lobes. 
The anus and resjtiratory orifice are under the posterior edge of 
the mantle, where, a little more deeply, Ave also find the pulmonary 
cavity. Close to them, on the right, opens the female organ of gene- 
ration ; that of the male, on the contrary, is under the right great 
tentaculum, the two openings being united by a furroAV, AAdhch extends 
along the under part of the whole of the right margin of the mantle. 
These animals, destitute of jaws, haA^e a muscular gizzard, folloAved 
by tAvo membranous stomachs. SeA-eral of them inhabit the sea- 
shore, but in places Avhere the ebb leaA^es them uncovered, so that 
they can readily breathe the natural airf. 
The acquatic Pulmonea, Avith complete shells, Avere also placed by 
Linnaeus in his genera Helix, Bulla and Valuta, from Avhich it has 
been found necessary to separate them. 
In the first Avere comprised the tAA’o folloAving genera, where Ave 
find the internal edge of the aperture crescent-shaped, as in Helix. 
Planorbis, Brug.-l 
The Planorbes had already been distingAiishcd from the Helices by 
Brugieres, and even preAuously by Guettard, on account of the slight 
* Onchidium, a name given to this genus, because the first species 
Buchan., Lin. Soc. Lond., V, 132) Avas tuberculous; I noAV know one that 
is smooth, the Onchidium Iceviguium, Cuv., and four or five that are tuberculous: 
Onch. Peronii, Cuv., Aim. du Mus., V, 6; — Onch. Sloanii, Cuv., Sloaue, Jam., pi. 
273, 1 and 2 ; — Onch. verrucuJutuni, Descr. de I’Eg., Moll. Caster., pi. ii. f. 3 ; — 
Onch. celficum, Cuv., a small species from the coast of Brittany. 
N. B. M. de Blainville has changed the name of Onchidium into that of Peronia, 
and applied the former to the Vaginula;. These Peronise he places among his 
Cyclobranchiata, but I can see no real dift'erence between their respiratory 
organ and that of the other Pulmoneie. 
t See Chamisso, Nov. Act. Alat. Cuv., XI, part I, p. 348, and Van Hassel, 
Bullet. Univers., 1824. Sept., Zook, 83. 
I Hel. vortex; — II. cornea; — H.spirorbis; — H. polggyra ;--II. contortu ; — //. 
initida ; — II. alba; — '!. simUis. 
See the quotations of Gmcl., and add, Draparnaud, pi. I, f. 39 — 51, and pi. ii. 
