GASTEROPODA NUDIBR ANCHIATA. 
39 
the external margin; this margin is enlarged, and as the animal 
renews it after each semi-whorl, the shell projects most on two oppo- 
site lines, and has a compressed appearance. 
They feed on aquatic plants in the Archipelago of India*. 
The two following genera were among the Volutae. 
Auricula, Lam. 
Differing from all the preceding aquatic Pulmonea in the columella, 
which is marked with wide and oblique flutings. Their shell is oval 
or oblong, the aperture elevated as in Bulimus, and the margin tumid. 
Several are large ; we are not certain whether they inhabit marshes 
like the Lymnaei, or their borders like the Succinese. 
Auricula myosotis. Drap. Ill, 16,17; Carychiuvi niyosotis, 
Feruss. The only species in France; the animal has but two 
tentacula, and the eyes are at their base ; from the shores of the 
Mediterranean!. 
CoNvovuLus, Lam. — Melampes, Movtf. 
Projecting folds on the columella, as in the Auriculae, but the margin 
of the aperture is not tumid, and the internal lip is finely striated ; 
the general form of the shell is that of a cone, of which the spire forms 
the base. They inhabit the rivers of the Antilles^. 
ORDER II. 
NUDIBRANCHIATAI!- 
The Nudibranchiata have neither shell nor pulmonary cavity, their 
branchiae being exposed on some part of the back. They all are 
hermaphroditical and marine animals, frequently swimming in a re- 
versed position, with the foot on the surface, concave like a boat, and 
using the assistance of the margin of their mantle and then tentacula 
as oars. In the 
* Helix scarabceus, L. 
•f- .Add, Volufa auris Midce, L., Martini, II, xliii, 436 — 38; Chemn.,X, cxlix, 
1395, 1396 ; — Valuta auris Juda, L., Martini, II, x'iv, 449 — 51 ; — Vol. auris Silent, 
Born., IX, 3 — 4 ; — Vol. (jlabra Alart II. xliii, 447, 448 ; — Vul. coffea, Cheinn., IX, 
cxxi, 1044. 
t Valuta minuta, L., Mart., II, xliii, f. 445, or Bulimus coniformis, Brug. ; — Bui. 
monile, Brug., Mart. Ib., f. 444 ; — Bui. ovulus, Br., Mart., Ib., 446. 
II My four first orders are united by M. de Blainville in what he terms a sub- 
class, designating them by the name of Paracephalophora Monoica. lie 
makes two orders of ray Nudibranchiata ; in the first, or the Cyclobranchiata, 
he places Doris and other analogous genera: in the second, or the Polybranchiata, 
are Tritonia and the following genera, which he divides into two families, according 
to the presence of two or four tentacula. 
