PTEROPODES. 
343 
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.* 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 Forarniniferes, because the cells 
communicate only by holes ; and he divides them into families from the manner in which the cells are 
arranged. When the cells are simple, and disposed spirally, 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 H. ammonoides ; and if the whorls rise up, as in the greater number of univalves, they are his H. 
turbinoides. 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 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 branchiae. 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 
Fig. 156.— Clio borealis. 2iy0j- voluminOUS. 
The most celebrated species {Clio borealis, 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 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 smaU 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 multilocular shells belong apparently to the testa- 
ceous Annelides ; while the curious observations of Dujardin seem to 
have proved that the great bulk of the Forarniniferes are not Mol- 
lusca, but animals related to the Infusoria. — Ann. des Sci. Nat, n. s. 
vol. V. et seq. — Ed. 
t M. de Blaiiiville unites my Pteropodes and Gasteropodes into 
one class, which he calls Paracephalophora, of which my Pteropods 
constitute his order Apurobranchiata. This order he divides into 
two families : — The Thecosomata, which have a shell ; and the Gymno- 
somata, which are shell-less. 
