PTEROPODES. 343 



connection with the septa of their shells, has occasioned them, like the genera which we have just 

 treated of, to he arranged in the series of Cephalopods ; hut this classification requires to he confirmed 

 hy more numerous observations hefore it can be considered as settled.* Linnaeus and Gmelin placed 

 the species known in their time in the genus Nautilus. M. d'Orbigny, who has studied them more 

 carefully than any one else, makes an order of them, which he calls Furaniiniferes, because the cells 

 communicate only by holes ; and he divides them into families from the manner in which the cells are 

 arranged. Wlien the cells are simple, and disposed spirally, the shells constitute his Helicosteyues, 

 which are subdivided ; for, if the whorls of the spire envelope each other, as is particularly the case with 

 the Camerines, he names them Helicostegues nautiloides ; if the whorls do not cover themselves, they 

 are H. ammonoides- ; and if the whorls rise up, as in the greater number of univalves, they are his H. 

 turbinoidea. The family Stycostegues is known by the simple cells being, as it were, threaded on a 

 single straight, or slightly curved axis. When the cells are disposed in two alternate rows, they are 

 then the Eiiallustegues. If the cells are gathered together in small numbers, and heaped up in a globular 

 shape, the family is the Agathistegiies. Lastly, in the Entomostegues, the cells are not simple, as in the 

 preceding families, hut are subdivided by transverse partitions, so that a section of the shell discovers 

 a sort of trelUs-work. 



THE SECOND CLASS OF MOLLUSCA.f 

 THE PTEROPODES. 



They swim, like the Cephalopods, in the sea, but cannot fix themselves there, nor creep, 

 from want of feet. Their organs of locomotion consist of fins only, placed at each side of 

 the mouth. The species known are of small size, and few in number. They are all herma- 

 phrodites. 



The Clio {Clio, Linn.; Clione, Pall.) — 



Have an oblong membranous body, without a cloak ; the head is formed of two rounded lobes, whence 



the little tentacula project; two small fleshy 

 lips, and a tongue, upon the front of the 

 mouth ; and the fins contain the vascular net- 

 work which supplies the place of branchiae ; 

 the anus, and the orifice of generation, are 

 under the right branchite. Some have as- 

 serted the existence of eyes. The viscera do 

 not nearly fill the exterior envelope. The 

 stomach is large, the intestine short, and the 

 i56.-ciio boreaiis Ijver voluminous. 



The most celebrated species (Clio boreaiis, Linn.) swarms in the northern seas ; and, from its abundance, be- 

 comes a food for the Whales, although no individual exceeds an inch in length. Brugui&re has observed a larger 

 species, in equal abundance, in the Indian Ocean. It is distinguished by its rose-colour, its emargiuate tail, and 

 its body separated into six lobes by as many grooves. 



It seems that we must also place here the 



Cymbulia of Peron, — 

 ^Vhich has a cartilaginous or gelatinous envelope in the shape of a boat, or rather of a shoe, roughened 

 with httle points arranged in longitudinal rows. The animal has two large vascular wings, which are 

 its branchiae and its fins ; and between them, on the open side, there is a third lesser lobe with three 

 points. The mouth, with two small tentacula, is between the wings, towards the closed side of the 

 shell ; and above are two minute eyes, and the orifice of generation, whence issues a penis in the form 



• Some of these multilocolar shells belong; apparently to the testa- I t M. de Blaiiiville unites my Pteropodes and Gasteropodcs inli, 



ceous Annclides ; while the curious observations of pujardiu seem to one class, which he calls Puraccphalophoru, of which my Pteropods 



have proved that the great bulk of the Foraminiferes are not Mol- I constitute his order ^porobranchiatit. This order he divides into 



a, but animals related to the Infusoria. — Ann. do Sa. Nat. a. s. J two families :— The Thecusomata, which have a shell ; and the Uj/iniiu- 



vol. v. et scq.— En. I somuta, which ;iru shell-less 



