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and size in different cases. It is exceedingly delicate, and could not 

 be found in the specimens first obtained, having probably been de- 

 stroyed or detached from the foot by the force of the water running 

 through the meshes of the net with which they were captured. Its 

 coexistence with an operculum shows that it is not a modification 

 of the latter. 



Of the Cheletropis Huxleyi, numerous specimens were found in 

 Bass's Straits and in the South Pacific, between Sydney and Lord 

 Howe's Island. 



After giving some details respecting the shell and the foot, the 

 aythor observes that the latter organ was destitute of float, at least 

 in the specimens he obtained, but was furnished with an operculum, 

 which, probably from its extreme thinness and smallness, had 

 escaped the notice of Professor Forbes. He then points out the 

 peculiarities of the respiratory apparatus. 



The portion of the mantle which forms the respiratory siphon, is 

 short, and its opposite edges are merely in apposition, without 

 organic union. The branchiae are of two kinds, covered and naked. 

 The covered gill is single but of considerable length. It is beautifully 

 pectinated, and fringed with long cilia, and, doubtless, represents 

 the respiratory organ of the pectinibranchiate Gasteropoda. The 

 basis of this part is a long and narrow strip of a tough and fibrous 

 material, folded upon itself into a series of loops invested with a 

 coating of epithelium, and richly ciliated along the free border. 

 The naked gills are four in number, similar both in situation and 

 character to those of Macgillivrayia. Each gill is of an oval or 

 elongated form, presenting a thin, frilled and corrugated border, 

 beset with long whip-like cilia. In the central parts muscular fibres 

 are distinctly discernible, some disposed lengthwise and others 

 transversely. 



The lingual strap is next described, as well as two file-like tri- 

 turating plates with which the mouth is furnished. 



The two tentacula of each side appear as it were enclosed in one 

 envelope, so as to form a single tactile instrument, which bears a 

 large dark eye on its outer side near the base. To this latter organ 

 the tegumentary covering forms a kind of cornea, beneath which is 

 a spherical lens resting on a mass of black pigment, both being in- 

 closed in a little sac ; and the optic nerve, emerging from the sub- 



