72 
PROFESSOR OWEN ON THE BELEMNITE. 
met with in connection with any of the simple or typical forms of fossil chambered 
shells, as the Orthoceratites , Baculites, Ammonites, &c. 
Reflecting on this marked difference in the anatomy of the Nautilus, I was led to 
perceive that, as this rare Cephalopod derived sufficient protection from its large and 
strong external shell, it might well dispense with that peculiar glandular apparatus 
which had before been deemed a common character of the Cephalopodal class ; whilst 
on the other hand, as the highly organized naked Cephalopods enjoy active powers 
of locomotion which would be incompatible with the incumbrance of a heavy external 
testaceous defensive covering, they required a compensatory endowment of the 
power of secreting an inky fluid, which, when alarmed, they might inject into the sur- 
rounding water and conceal themselves by the dusky cloud thus occasioned. But the 
branchial character of the naked order of Cephalopods is an essential condition of 
their muscular powers ; the presence of an ink-bladder, therefore, in the extinct 
Belemnites, would have implied the internal position of the shell, even if other proof 
had been wanting ; and, by the laws of correlation, it implies likewise the presence 
of the muscular forces for rapid swimming, and the concomitant conditions of the 
respiratory, the vascular and the nervous systems. Connecting, therefore, all these 
considerations with the detection of the ink-bag in the shell of the Belemnite, 1 
felt justified in referring the Belemnites, and likewise the Spirula, on account 
of the ascertained internal position of its shell, to the Dibranchiate order; and I 
therefore separated these chambered and siphoniferous shells from the Nautilus and 
the Ammonites, in the classification of the Cephalopoda submitted to the Zoological 
Society in February 1836*. 
But the true grounds of this separation seem not to have been appreciated or un- 
derstood by some Palaeontologists. Professor Phillips, for example, in his excellent 
article on Turrilites, in the part of the Penny Cyclopaedia published in January 1843, 
has observed, “ The relations of Turrilites, Scaphites, Baculites and Hainites to Am- 
* Zoological Transactions, ii. pp. 127, 12.0. “ The Cephalopods with internal chambered shells, heretofore 
classed with the siphoniferous Cephalopods, which constitute the preceding order, I would join with all the other 
naked Cephalopods, to form a second order, under the term Dibranchiata, having reference to the number of gills, 
viz. two. This number is constant in all the ‘ Seiches’ of Cuvier, and is associated with the presence of two 
branchial hearts, besides the single systemic heart, and with an ink-bag : there can be little doubt that the 
same type of structure is exemplified in the Spirula, from what has been determined respecting its external 
characters 3 .” 3 “The discovery by Dr. Buckland of the remains of the ink-bag in the extinct Belemnites, 
justifies the conclusion from the laws of coexistence, that these Cephalopods also possessed two gills and two 
branchial hearts.” In the same year, 1836, the Number of the Cyclopaedia of Anatomy and Physiology was 
published, containing my Article f Cephalopoda,’ in which it is argued of the Belemnites : — “ As it is certain that 
the animals of this family of extinct Cephalopods possessed the ink-bag, they must consequently have been 
enveloped by a muscular mantle ; and we may, therefore, infer that they resembled the Dibranchiates in their 
locomotive and respiratory organs, and consequently in the general plan of their organization. In the structure 
and position of their siphoniferous camerated shell, they are intermediate to Spirula and Sepia, and as the 
animal of Spirula is proved to be a Decapod, the probability is very strong that the animal of the Belemnite was 
of the same type.” — p. 520. 
