PTEROPODA. 21 



three points. The mouth with two small tentacula is situated be- 



ii tin- wings towards the closed >ide of the shell and above two 



: ! ryes, and the genital aperture, whence issues a small penis in 



t!n shape of a little proboscis. It is so diaphanous, that the heart, 



brain, and viscera can be distinguished through the envelopes*. 



PNEUMODERMON, Cuv. 



I Pneumoderma begin to be a little further removed from the 



. Their body is oval, without a mantle and without a shell ; the 



are attached to the surface, and composed of little laminae, 



arranged in two or three linos so disposed as to form an H on the 



part opposite to the head The fins are small; the mouth which is 



t'nrjushed \\-ith two small lips and two bundles of numerous tentacula, 



terminated by a sucker, has a little lobe or fleshy tantaculum 



beneathf. 



Pneumodermon Peronii, Cuv. Ann. du Mus., IV, pi. 59 ; 

 and Peron, Ib., XV, pi. 2. Not more than an inch long. The 

 ipeciea known was captured in the Ocean by Peron. 



LlMACINA, CUV. 



The Limaein.np, according to the description of Fabricius, should have 

 been closely related to the Pneumoderma ; but their body terminates 

 in a spirally convoluted tail, and is lodged in a very thin shell formed 

 by one whorl and a half, unbilicated on one side, and flattened on the 

 oilier. The animal uses its shell as a boat, and its wings as oars, 

 whenever it wishes to navigate the surface of the deep. 



The species known Clio helicina, Phips and Gmel. ; Argonauta 

 nrctica, Fab., Faun. Groenl., 387, is almost as common on the 

 Arctic seas as the Clio boreaKs, arid is considered as forming 

 one of the chief sources of food for the Whale J. 



HYALEA, Lam,, CAVOLINA, Abildg. 



Have two large wings ; no tentacula; a mantle cleft on the sides, 

 lodging the branchiae in the bottom of its fissures, and invested by a 

 .shell also cleft laterally, the ventral face of which is arched, and the 

 dorsal flat and longer than the other; the transverse line which 

 unites them behind, is furnished with three sharp dentations. When 

 alive, the animal thrusts several appendages, that are more or less 



* Sec Prron, Ann. Mus., XV, pi. iii, f. 10 11. N. B. in the fig. of CymbvKa, 

 iri\cii by IHaimille, Malar., XIAI, tlie position of the animal in the shell is directly 

 ilir r i !H- true one. Our description is founded upon the recent and re- 



: ol>M-r\ations of M. Laurillanl. 



de Illainville once thought that the fins supported the branchial tissue, and 

 that what I have considered as branchisc is another kind of fin. In this case the 

 analoiry with the Clios would have been greater ; but ^ince then, (Malacol., p. 483) 

 that .- as adopted ray views. 



i not sure that the animal drawn by >Yorc->\. of which de Blainville 

 \lviii. bis, f. 5) makes his genus SIMRATELLA, is, as be thinks, the same 

 as those of Phips and Fabri< 



