OWEN ON THE BELEMNITE. 125 



nite : next, in reference to the entire shell we must admit 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 Belem- 

 nite ; the convex posterior broad plate of horny with friable cal- 

 careous matter is analogous to the capsule of the phragmocone ; 

 but its margins, instead of being approximated and soldered to- 

 gether, are free and lateral in position ; the congeries of trans- 

 verse plates lodged in the concavity of the nucleus and of the 

 foregoing semi-capsule of the cuttle-bone answer to the chambered 

 phragmocone 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 re- 

 lative size, shape, and position of the fins, the Belemnite must 

 have most nearly resembled the species of the existing Rossia and 

 Sepiola ; but it differed in the more elongated and slender body. 



The character of the formidable hooks supported by the aceta- 

 bula of the arms is now exclusively manifested by the genus 

 Onychoteuthis. 



Thus the extinct Belemnite combined characters at present di- 

 vided amongst four distinct genera of Dibranchiate Cephalopods, — 

 Spirula, Sepia, Sepiola, and Onychoteuthis. 



But notwithanding the uncinated character of the arms the 

 balance of the natural affinities seems 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 af- 

 finity, tending to complete the reticular inter-dependencies of the 

 Cephalopods, do not disturb, but confirm, the position of the Be- 

 lemnite in the linear series of the genera of that class proposed 

 in 1836. 



The Belemnite, with the advantage of its dart-shaped and well- 

 balanced shell, must have enjoyed the power of swimming back- 

 wards and forwards by the action of its cephalic and pallial fins 

 with greater vigour and precision than the modern Decapod 

 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 cannot doubt but that, like the uncinated Calamaries of the 

 present seas, the ancient Belemnites were in their day the most 

 formidable and predaceous of Cephalopods. 



D. T. A. 



