CEPHALOPODA. 603 



common cuttle-fi^h : the lateral fins of this species extend from the 

 apex to near the base of the mantle. The nucleus, or terminal spine 

 of the cuttlebone corresponds with the spathose guard of the Belem- 

 nite : the convex posterior broad layer of friable calcareous and 

 horny matter is homologous with the enveloping cone; but its 

 margins, instead of being approximated and soldered together, are 

 free and lateral in position : the successive plates, embedded in its 

 concavity, answer to the camerated cone of the Belemnite ; but, in- 

 stead of being perforated by one or many siphons, they are connected 

 with each other by a series of minute undulating lamellae. 



Thus at length has been obtained the proof of the dibranchiate nature 

 of the Belemnite, and we learn from the same ocular evidence that it 

 combined characters at present divided between three distinct genera 

 of the order ; namely, first the calcareous internal chambered shell, 

 to which the Sepia offers the nearest approach ; secondly, the for- 

 midable hooks of the arms, which characterise the modern genus 

 Onychoteuthis ; and, thirdly, the limited attachment of the lateral 

 fins to a position a little in advance of the middle of the body, as in 

 the Sepiola. 



The Belemnite, having the advantage of its dense but well-balanced 

 internal shell, must have exercised its power of swimming backwards 

 and forwards, which it possessed in common with the modern decapod 

 Dibranchiates, with greater vigour and precision. Its position was 

 probably more commonly vertical than in its recent congeners. It 

 would rise swiftly and stealthily to infix its claws iir the belly of a 

 supernatant fish, and then dart down and drag its prey to the bottom 

 and devour it. We cannot doubt at least but that, like the hooked 

 Calamaries of the present seas, the ancient Belemnites were the most 

 formidable and predacious of their class. 



LECTURE XXIV. 



CEPnALOPODA. 



The deductions which were founded on the modifications of the 

 chambered siphoniferous shell and other enduring remains of the 

 very remarkable extinct genus which occupied our attention at the 

 close of the last lecture, obliged me frequently to refer to the type of 

 structure which characterises the Dibranchiate order of Cephalopods, 

 and which places these Mollusks not only at the head of that division 



