GASTEROPODA HKTEROPODA. 
49 
G. Meckelii ; Rosse, Diss. de Pteropodum Ordine, Halae, 
J813, f. 11 — 13; and Blainv. Malacol., jd. xlv, f. 5; or Clio 
amati, Delle Chiaie, Memor., pi. ii, f. 1 — 8. A small animal an 
inch long, and two broad, the wings being extended. From the 
Mediterranean. 
For the present, and until our anatomical studies are more ex- 
tended, we are under the necessity of placing in this order of Tecti- 
branchiata, and even very close to the ideurobranchus, the singular 
genus. 
Gastkoplax, Blaimi . — Ombp,elles, of Lam. 
The animal is a lai’gc and circular mollusca, wliose foot projects con- 
siderably beyond the mantle, and its upper surface is studded with 
tiibercles. I'he viscera are in a round, superior, and central part. 
The mantle is only visible by its slightly projecting and trenchant 
edges, along the whole of the front and of the right side. The lamel- 
lated pyramidal branchiae, like those of the Pleurobi’anchus, are under 
this slight margin, and behind them is a tubular anus. Under this 
same margin and forwards, are two tentacula, longitudinally cleft, as 
in Pieurobranchiis, at whose internal base are the eyes ; between 
them is a kind of proboscis, which may possibly be the organ of 
generation. There is a large concave space in the anterior margin of 
tlie foot, the edges of whicii are susceptible of being drawn up like the 
mouth of a purse, and at the bottom of which is a tubercle, pierced 
by an oriticc, which periiaps is the mouth, and surmounted by a 
fringed membrane. The inferior surface of the foot is smooth, and 
serves the animal to crawl on, as in the other Gasteropoda. 
The animal carries a shell vrhich is stony, flat, irregularly rounded, 
thickest in the middle, with trenchant edges, and marked with slightly 
concentric stricC. It was at first thought to be attached to the foot, 
but more recent observation has proved that it is on the mantle, and 
in the usual place*. 
ORDER V. 
HETEROPODA, Lam[. 
The Heteropoda are distinguished from all other mollusca by 
* 111 the specimeu from the British Museum described by M. de BhiinviUe, 
Bullet. Phil., 1819, p. 178 ; by the name of Gastropl.^x, the shell is, in fact, 
attached to the under part of the foot, and by what means it is difficult to determine ; 
the mantle, however, is so thin, that it seems as if it must have been protected by 
the shell. M. Rcynaud has just brought to France a specimen which had lost its 
shell, but where, it appears, traces of the membranes which attached it to the 
mantle can be perceived, notwithstanding which, no remains of muscles are visible. 
A similar shell is also found in the Mediterranean ; its animal, however, has not yet 
been observed. 
i- M. de Blainville makes a family of the Heteropoda, which he names Nec- 
TOPODA, and unites them in his order of the Nuclkobu.\nchiata with another 
family that he calls Pteropoda, and which, of all my Pteropoda, only includes the 
Limacina. He joins the Argoruiuta with it, on account of some conjecture, of which 
I am ignorant. 
VOL. III. 
K 
