v. 



BRITISH FOSSILS. 



On the STRUCTURE of the BELEMXITUXE ; with a description of 

 a more complete Specimen of Belemnites than any hitherto 

 known, and an account of a New Genus of BELEMNiTnxfi, 

 Xiphoteuihis, by THOMAS H. HUXLEY, F.R.S., Professor of 

 Natural History, Royal School of Mines. 



THE fossil shell called Belemnites consists fundamentally of (1) a 

 hollow cone, the phragmoconus, with a thin, shelly, wall which may be 

 termed the conotheca, and which is divided by transverse septa, more 

 or less convex towards the apex of the cone, and concave towards its 

 base, into chambers, or loculi. Each septum is traversed, close to the 

 conotheca, in a direction which corresponds with the median ventral 

 line of the body, by a canal, the siphunculus. More or less extensively 

 enveloping the apical part of the phragrnocone is (2) a more solid body, 

 the guard, or rostrum, composed of calcareous matter arranged in prisms, 

 or fibres, perpendicular to the planes of lamellae. These are disposed 

 concentrically around an axis, the so-called apical line, which extends 

 from the extremity of the phragmocone to that of the rostrum. 



All observers are agreed as to the presence of the parts hitherto 

 mentioned in a Belemnite, but a great diversity of opinion prevails 

 respecting the nature, and indeed the existence, of a third constituent 

 of the fossil, the so-called " pen " or " osselet." As the part which 

 commonly goes by the name of " pen " in the Belemnite, however, 

 corresponds to only a part of the structure already known as the 

 " pen " in recent Cephalopoda, I shall endeavour to avoid ambiguity, 

 by using for it the appellation of pro-ostracum. 



In a paper " On the discoveiy of a new species of Pterodactyle, and 

 ;i nl*o of the faeces of the Ichthyosaurus, and of a black substance re- 

 " sembling Sepia or Indian ink, in the Lias of Lyme Regis," read before 

 the Geological Society, on the 6th February 1829, by Dr. Buckland, 

 the following passage occurs. 



" 3. Fossil Sepia. An indurated black animal substance, like that 

 in the ink-bag of the cuttle fish, occurs hi the Lias at Lynie Regis ; 

 and a drawing made with this fossil pigment, three years ago, was 

 pronounced by an eminent artist to have been tinted with sepia. It 

 i> nearly of the colour and consistence of jet, and very fragile, 

 with a bright splintery fracture ; its powder is brown, like that of 

 painters' sepia; it occurs in single masses, ' nearly of the shape and 

 size of a small gall-bladder, broadest at the base, and gradually con- 

 tracted towards the neck : these are always surrounded by a thin 

 nacreous case, brilliant as the most vivid Lumachella ; the nacre 

 seems to have formed the lining of a fibrous, thin, shelly substance, 

 \vhich, together with this nacreous lining, was prolonged into a hollow 

 cone like that of a belemnite, beyond the neck of the ink-bag ; close 



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