CLASS CEPHALOPODA. 17 
They vary in a remarkable degree as to their general form, 
the number and relative position of the chambers, &c. One 
or two species, in which alone the animals have been observed, 
appeared to present a small oblong body, crowned by numerous 
red tentacula, which, added to the septa of the shell, have 
caused them to be placed immediately after the cephalopoda, 
like the genera just mentioned. This arrangement, however, 
requires to be confirmed by more numerous observations, 
before we can consider it as final. 
Such of these species as were known in the time of Linneus 
and Gmelin, were placed by those naturalists among the nau- 
tili. M. D’Orbigny, who has exceeded every other person in 
attention to this subject, forms them into an order which he 
calls FORAMINIFERA, on account of the only communication 
between the cells being by means of holes, and divides them 
into families according to the manner in which the cells are 
disposed. When the cells are simple and spirally arranged, 
they constitute his HELICOSTEGA, which are again sub- 
divided. Ifthe whorls are enveloped, as is particularly the 
case in the nummulites, they become his HELICOSTEGA 
NAUTILOIDA. 
If the whorls do not envelope each other, they are the 
HELICOSTEGA AMMONOIDA. 
If the whorls are elevated, as in most of the univalves, they 
are the HLELICOSTEGA TURBINOIDA. 
Simple cells may also be strung upon a single straight or 
slightly curved axis, constituting the family of the STYCOSTEGA. 
Or they may be arranged in two alternate series, when they 
become the ENALLOSTEGA. 
Or a few of them may be collected and united as in a pel- 
let, forming the AGATHISTEGA. 
Finally, in the entomostega, the cells are not simple, as in 
the other families, but are sub-divided by transverse septa in 
such a way that a section of the shell exhibits a sort of trellis. 
VOL. XII. c 
