Class 2. 



PTEPtOPODES. 



335 



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

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

 by more numerous observations before it can be considered as settled.* Linnajus and Gmelin placed 

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

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

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

 arranged. AYhen the cells are simple, and disposed spirally, the shells constitute his Ilelicustcf/ues, 

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

 the Camerines, he names them Helicosteyues 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 //. 

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

 shape, the family is the Agathistegues. Lastly, in the Entomostegues, 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 trellis-work. 



THE SECOND CLASS OF MOLLUSCA.f 



THE PTEROPODES. 



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

 from want of feet. Then* 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 arc all herma- 

 phrodites. 



The Clio (C/io, Linn. ; CUone,Va\\.) — 



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 branchia; ; 

 the anus, and the orifice of generation, arc 

 under the right branchise. Some have as- 

 serted the existence of eyes. The viscera do 

 not nearly fill the exterior envelope. The 

 stomach is large, the intestme short, and the 

 liver voluminous. 



The most celebrated species (Clio boreaUs,'L\m\.) swarms in the northern seas; and, from its abundance, be- 

 conies a food for the Whales, alihoug-a no individual exceeds an inch in length. Bruicuicre has observed a larger 

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

 its body separated into six lobes by as many grooves. 



It seems that we must also place here the 



Cymbulia of Peron, — 

 Which 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. 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 



Vig, 15G. — Clio borcalis 



* Sume of these mullilocular sliclls belong apparently to the tcita- 

 ccous Annclides ; while the curiuus ohservations of Dujardin seem to 

 imve proved that the great bulk of the Koraminifercs are not Mol- 

 lusca, but animals related to the Infusoria.— Wkk. des Sci. M'lit. n. s. 

 Tul. V. et 8cq.— Kd. 



t M. de Blainville unites my Pteropodes and Gasteropodes into 

 one class, which he calls Ptirncephalupfiura, of which my Pteropods 

 constitute his order j-lporobratic/iiattt. This order he divides into 

 two families:— Tlie Thecosomata, which have a shell; and the Oymni- 

 tomata, which are sbell-lesi. 



