122 GEOLOGICAL MEMOIRS. 



dition of their muscular powers, would alone have implied an 

 internal shell, the presence of muscular forces for rapid swimming, 

 and the concomitant conditions of the respiratory, the vascular, and 

 the nervous systems. The reference of the Belemnite to the Di- 

 branchiate order, and the separation of their genus from NoMtilus 

 and Ammonites^, was the conclusion arrived at by these consider- 

 ations ; and the specimen lately presented to the Hunterian museum 

 by the Marquis of Northampton exhibits a proof of the correct- 

 ness of this view, since, besides the phragmocone, it shows 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. It is evident also from this specimen, that in the proportion 

 of the body, and in its elongated form, the Belemnite resembled the 

 Onychoteuthis and most of the modern Decapoda. 



Another specimen in the possession of Mr. Pratt exhibits, to- 

 gether with a portion of the muscular mantle and other parts, the 

 ink-bag and duct, and the two fins. The reservoir of ink is situ- 

 ated two lines within the aperture of the phragmoconic capsule ; it 

 is of an oval form and jet-black colour ; the inspissated ink is very 

 hard, brittle, and splintering, but when reduced to a fine powder it 

 presents a dark brown hue; and used as a pigment, works as 

 smoothly as Roman Sepia, but with a deeper tint. The parts re- 

 garded as fins are flattened fibrous bodies, with well-defined semi- 

 oval, external, and, apparently, free margins. The large end of the 

 border is the anterior one, where the fin is broadest, and it gradu- 

 ally becomes narrow posteriorly. 



It is interesting to find a rounded contour associated with an 

 advanced position of the lateral fins in the ancient Belemnites, the 

 rhomboidal form being most common in those fins placed at the 

 end of the body ; the only exception, indeed, to this being presented 

 by the Loligopsis, which has terminal and rounded fins. 



hi Mr. Pratt's specimen, at the middle of the visceral mass, be- 

 tween the two lateral fins, there lies a compressed body of a horny 

 texture and sub-bilobed form, on which may be clearly distin- 

 guished strias passing outwards in opposite directions from a 

 middle line, and diverging from each other in their course. It 

 resembles the fibres of the digestive muscle in the gizzard of 

 the Nautilus and other Cephalopods ; and this apparent remnant 

 of the stomach lies about half an inch in advance of the ink- 

 bladder, in a position corresponding with that of the gastric organ 

 in naked Cephalopods. 



There is strong negative evidence that the Belemnite possessed 

 horny mandibles like the other naked Cephalopods, since no cal- 

 careous beaks or Rhyncholites have been discovered associated 

 with the specimens from the Oxford clay, or with those from the 

 Lias. 



The thickness of the layer of dried and compressed grey fibrous 

 matter to which the mantle is reduced is half a line, and we may 

 hence infer that in its soft and recent state, when permeated by its 



