ORDER PULMONARIA. ou 
And those in which the extremity of the columella is curved 
towards the inside of the aperture (Polyphemus, Mont.), the 
last whorl is higher. (Bulimus glans, Brug.) 
The AQUATIC PULMONARIA 
Have but two tentacula, as already stated ; they are continu- 
ally compelled to rise to the surface for the purpose of breath- 
ing, 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, Buchanan. 
A broad fleshy mantle, in the form of a shield, overlapping 
the foot at all points, and even covering the head when it 
contracts; two long retractile tentacula; and on the mouth an 
emarginated veil, formed of two triangular and depressed 
lobes. 
The anus and respiratory orifice are under the posterior 
edge of the mantle, where, a little more deeply, we also find 
the pulmonary cavity. Close to them, on the right side, opens 
the female organ of generation ; that of the male, on the con- 
trary, is under the right great tentaculum, the two openings 
being united by a furrow, which extends along the under part 
of the whole right margin of the mantle. These mollusca, 
destitute of jaws, have a muscular gizzard, followed by two 
membranous stomachs. Several of them inhabit the sea-shore, 
but in places where the ebb leaves them uncovered, so that 
they can readily breathe the air as is natural to them. 
The name of ONCHIDIUM was given to this genus because 
the first species (Onchidium typhe, Buckan.), was tubercu- 
lous. I now know one that is smooth (O. levigatum, Cuv.), 
and four or five that are tuberculous. 
The aquatic pulmonaria with complete shells were also 
VOL, XII. D 
