GASTEROPODA HETEROPODA. 49 



O. Meckelii ; Rosse, Diss, de Pteropodum Ordine, Halae, 

 J 813, f. 11—13; and Blaiiiv. Malacol., pi. xlv, f. .5; or Clio 

 amali, 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 tlie 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 pleurobranchus, the singular 

 genus. 



G.vsTROi'LAX, Blalnv. — Ombrelles, of Lam. 



The animal is a large and circular mollusca, whose foot projects con- 

 sideral)ly be5^ond the mantle, and its upper surface is studded with 

 tubercles. The 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 tlie front and of the right side. The lamel- 

 iated pyramidal branchiae, like those of the Pleurobranchus, 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 Pleurobranchus, 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 

 the foot, the edges of which are susceptible of being drawn up like the 

 mouth of a purse, and at the bottom of which is a tubercle, pierced, 

 by an orifice, which perhaps 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. 



Tlio animal carries a shell which is stony, flat, irregularly rounded, 

 thitikest in the middle, with trenchant edges, and marked with slightly 

 concentric striie. 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 



* In the specimen from the British Museum described by M. de Blainville 

 »uUet. Phil., 1819, p. 178 ; by the name of Gastroplax, 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. Reynaud has just brought to France a specimen which had lost its 

 sliell, but where, it appears, traces of the membranes which attached it to the 

 Kiantle can be perceived, notwithstanding which, no remains of muscles are visible. 

 A similar sliell is also found in the Mediterranean ; its animal, however, has not vet 

 been observed. ' 



t M. de Blainville makes a family of the Heteropoda, which he names Nec- 

 TOPODA, and unites them in his order of the Nucleobranchiata with another 

 family that he calls Pteropoda, and which, of all my Pteropoda, only includes the 

 .Umanna. He joins the Argomula with it, on account of some conjecture, of which 

 1 aBi ignorant. 



y-OL. ill. 



