82 
PROFESSOR OWEN ON THE BELEMNITE. 
or higher order of Cephalopods, in which its right of place can no longer be disputed, 
we shall first recognize in the outwardly concave plates and margino- ventral siphon 
of the chambered shell of the Spirula, the analogue of the hydrostatic part of the shell 
or phragmocone of the Belemnite : next in reference to the entire shell we must 
admit, agreeably with the opinion of De Luc, Miller, De Blainville and Buck- 
land, that the Sepia or common Cuttle Fish, most nearly resembles the Belemnite 
in the general structure and position of its complex calcareous plate. The nucleus 
or terminal spine of the sepium or cuttle bone corresponds with the terminal 
spathose guard of the Belemnite ; the convex posterior broad plate of horny with 
friable calcareous matter is analogous to the capsule of the phragmocone ; but its 
margins, instead of being approximated and soldered together, are free and lateral 
in position : the congeries of transverse plates, lodged in the concavity of the nucleus 
and of the foregoing semi-capsule of the cuttle-bone, answer to the chambered phrag- 
mocone of the Belemnite, but, instead of being perforated by one or many siphons, 
they are entire and connected with each other by a series of minute undulating lamellae 
perpendicular to their plane. 
The lateral fins of the Sepia are narrow, and extend, as is well known, from the 
apex of the mantle to near its base ; while the fins of the Belemnite were relatively 
shorter and broader, and situated a little in advance of the middle of the body. In 
the relative size, shape, and position of the fins, the Belemnite must have most nearly 
resembled the species of the existing genera Rossia and Sepiola, but it differed in 
the more elongated and slender body. 
The character of the formidable hooks, supported by the acetabula of the arms, 
is now exclusively manifested by the genus Onychoteuthis. 
Thus the extinct Belemnite combined characters at present divided amongst four 
distinct genera of Dibranchiate Cephalopods, Spirula, Sepia, Sepiola, and Onycho- 
teuthis. But, notwithstanding the uncinated character of the arms, the balance of 
its natural affinities seems to me still to preponderate in favour of its position as a 
transitional link between Spirula and Sepia : and the additional facts which we have 
now unexpectedly gained, while they show new and unsuspected radiations of affinity 
tending to complete the reticular interdependencies of the Cephalopods, do not dis- 
turb, but confirm the position of the Belemnite, in the linear series of the genera of 
that class which I proposed in 1836. 
The Belemnite, with the advantage of its dart-shaped and well-balanced shell, must 
have enjoyed the power of swimming backwards and forwards by the action of its 
cephalic and pallial fins, with greater vigour and precision than the modern Deca- 
pod Dibranchiata. The position of the animal was, most probably, more habitually 
vertical than that of its recent congeners. Thus placed, the Belemnite, in quest of 
prey, would rise swiftly or stealthily to infix its claws in the belly of a supernatant 
fish, and then dart down, and drag its prey to the bottom and devour it. And we 
