522 HABITS OF PTEROPODS. 



freely about, without being encumbered with a dense, 

 heavy skeleton. M. Rang offers, as a generic character, 

 the constant presence of asperities on the mantle ; but 1 

 think this will hardly serve, as I have figured a species 

 from the South Atlantic, which I believe to be new, which 

 is perfectly smooth, and totally devoid of any processes 

 on the mantle. 



The mantle of C'leodora, like that of Hyalcea, is very 

 much dilated, and forms two swimming appendages, and 

 the intermediate lobe is semicircular; but there are no 

 elongated lateral expansions similar to those that emerge 

 from the slits in the side of Hyalaa. In many figures of 

 these animals, the swimming lobes are represented as 

 varying in form in different species, but from my obser- 

 vations, I should say that the lobes, Vandykes, and fold- 

 ings of the margin, are purely accidental contractions, and 

 that commonly the margins are entire. The animal of 

 Cleodora Byzantium has, when alive, the two swimming 

 expansions very much elongated laterally, rather slender 

 and rounded at their free extremities. In C. cuspidata, 

 they are shorter and rounded. The Hylcece, no doubt, 

 like the Amphibia among the reptiles, respire by the entire 

 cutaneous surface, which is so soft and permeable; al- 

 though, it is true, they have distinct breathing organs, 

 disposed in the form of an oval ring, between two layers 

 of the mantle on the dorsal region, which are open, to 

 receive currents of water transmitted by the lateral aper- 

 tures of the shell. The long, loose, lateral, pallial prolong- 

 ations, which these testaceous Pteropods protrude from 

 the lateral fissures of the shell, do not appear to be of 

 much use in guiding or propelling, which functions are 



