PTEROPODES. 



343 



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

 treated of, to be arranged in the series of Ccphalopods ; but this classification requires to be confirmed 

 by more numerous observations before it can Ije considered as settled.* Linnaeus and Gmelin placed 

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

 carefully than any one else, rnakes an order of tliein, which he calls For ammif even, because the cells 

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

 arranged. When the cells are simple, and disjiosed sinniUy, the shells constitute his Helicostegues, 

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

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

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

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

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

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

 shape, the family is the Agatlmtegu.es. Lastly, in the Eatomostegues, the cells are not simple, as in the 

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

 a sort of treUis-work. 



THE SECOND CLASS OF MOLLUSCA.t 



THE PTEROPODES. 



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



from want of feet. Their orgaus of locomotion consist of tins only, placed at each side of 



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



phi'odites. 



The C:lio {Clio, Linn.; Clione, Pall.)— 



lla\t in blono; meml)rauous 1 jd\ v\itl ut a cljik the head is formed of two rounded lobes, whence 



the little tcntacula 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 branchia; ; 

 the anus, and the orifice of generation, are 

 under the right branchiae. Some have as- 

 serted the existence of cyus. The \iscera do 

 not nearly fill the exterior envelope. The 

 stomach is large, the intestine short, and the 

 liver voluminous. 



The most celebrated species {Clio borcalis, Linn.) swarms in the northfrn seas ; and, from its abundance, be- 

 comes a t'uod for the Whales, althougii no individual exceeds an iiicii in leii,:2;th. Urui^uiLTe has observed a larger 

 .sjiecies, in equal abundance, in tlie Indian i »cean. It is distin;;'Lii6licd by its ruse-coluur, 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, — 

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

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

 it.s hranchicc and its fins; and between them, on the open side, there is a third lesser lobe with three 

 points. The mouth, with two small tcntacula, 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 



iinc of these multilocular shtlls belong apparently to the Icsta- 

 A-iiiiL-lides ; while tlic curious oliservutions of Dujardin sci'iii tu 

 ,n.vL-ii that tlie i,Tfat bulk of ilie Foran.iiiifcrc's are not Mol- 

 l.ul fi-iimals TL-lated to (lie Infusoria,— .;;;», dta Sa. .\at. n. S. 

 Ll sci[,— En. 



t M. de Blainville unites my Pteropodea and Gasteropodea Into 

 me (.lass, ivliich tit tails Piiniccphalophora, of which my Ptero|")da 

 :oiistitute his order .-Iporobrarichiain. Thia order he divides into 

 wo families : — The Tliecosomata, ishich Ijave a shell ; ami the Gpnuiu- 

 om-iiii, which :vre shell-less. 



