PROFESSOR OWEN ON THE BELEMNITE. 
73 
monites is very obvious; and, as through Goniatites, this great extinct group is cer- 
tainly connected to the living and extinct Nautili, Mr. Owen has ventured to include 
them all in the Tetrabranchiate Cephalopoda, leaving Spirula and the Belemnites 
with Sepia and the Di branchiate types. However this may be, the determination 
of the relative affinities among the numerous fossil Cephalopods, a point of great im- 
portance, must be worked out with the help of other considerations than the respira- 
tory system.” In the memoir on the ‘ Classification of Cephalopoda ,’ above cited, it 
will be found that many other considerations than those of the respiratory system, 
and of equal importance with them, influenced me in forming an opinion ot the na- 
tural position of the Belemnites in the class Cephalopoda. 
Leopold Von Buch, who believed that he could trace in certain slabs containing 
Belemnites the impressions of the Cephalopods to which they belonged, concluded 
“ that the body of the animal enveloped the greater part of the shell, and exceeded 
its length by eight or ten times*.” Other considerations taken from the shell itself 
prove, as has already been shown, that it was wholly internal. 
The specimen-j' presented to the Hunterian Museum by the Marquess of North- 
ampton, exhibits the phragmocone, the muscular mantle, a small part of the head, 
and a greater or less proportion of six of the cephalic tentacula which are armed 
with horny hooks in a double alternate series, as in the Onychoteuthis gigas. 
The phragmocone with the soft parts of the Belemnite has been detached from the 
guard probably soon after death ; and the whole squeezed nearly flat after becoming 
interred in the laminated clayey matrix. The resistance of the ink-bag ( n ) with its 
inspissated and indurated contents, has led to abrasion and loss of the walls of the 
part of the phragmocone covering it, and it seems to have been pressed downwards 
through one or two of the basal partitions deeper into the sheath than was natural, 
or than it is situated in other specimens. The capsule of the phragmocone extends 
about one-third of an inch beyond the ink-bag, and terminates by a well-defined 
border. The smooth surface of its opake white external calcareous layer is well 
preserved over nearly the whole of this part. The muscular tunic of the mantle (d) 
appears to commence at the peristome ; it seems to have first undergone the change into 
adipocire and then to have become so brittle as to crack and break instead of bend- 
ing to the pressure ; the course of the muscular fibres is plainly visible ; all those on 
the outer surface of the mantle which is presented to the observer, are transverse or 
circular; this surface is smooth, and the course of the fibres more feebly indicated; 
in the few places where the upper side of the mantle is broken away, and the inner 
surface of the opposite side shown, the arrangement of the transverse fasciculi is 
more strongly displayed. 
In the length as compared with the breadth of the mantle, the Belemnite is 
shown by this beautiful specimen to have had the same elongated form of body as 
the Onychoteuthis and most modern Decapoda. 
* Oken’s Isis, Bd. xxi. p. 438. 
MDCCCXLI V. 
L 
t PL III. 
