CEPHALOPODA. 113 



like the phragmocones of the associated Belemnites, both in 

 structure and proportions, that they were originally described 

 by me as such,* and they give good evidence of the close 

 affinity of the cephalopod possessing them to the true Belem- 

 nite : hitherto they have only been noticed in the laminated 

 Oxford clay of Wilts, and the equivalent lithographic shales 

 of Solenhofen. 



Species of Belemnite are found in all the oolitic and cre- 

 taceous strata, from the lowest lias to the upper chalk. The 

 shell, in its ordinary imperfect state, is a cylinder pointed at one 

 end (fig. 34, i), and truncated or excavated by a funnel-shaped 

 cavity {alveolus, ib. p) at the other, and has a radiating fibrous 

 structure, with less distinct concentric laminae of growth. But 

 even this "guard," which corresponds simply to the "mucro" 

 of the cuttle-bone (ib. 5), exhibits such remarkable modifica- 

 tions of form, that nearly 100 species have been founded upon 

 no higher evidence. In some Belemnites of half an inch 

 diameter, the guard is scarcely an inch longer than the phrag- 

 mocone ; whilst in others it attains a length of ten inches, and 

 is tubular, as in B. acuarius. Some are fusiform, others later- 

 ally compressed ; some have a longitudinal groove extending 

 from the apex along the upper or under side, and in others 

 the apex is furrowed laterally as well. The Belemnites of the 

 chalk have been called Belemnitcllce (d'Orb.), because they 

 have a slit in the ventral side of the alveolar border of the 

 guard ; their external surface also exhibits more distinct 

 traces of vascular impressions. 



Specimens of Belemnite have been discovered in which the 

 guard had been broken during the lifetime of the animal ; but 

 the broken portions, being held together by the investing 

 organized integuments, had been re-united by the deposition 

 of new layers of the fibrous structure peculiar to the guard. 

 Several examples of Belemnites, with the apex injured and 



* Philosophical Transactions, 1844 ; and Cat. Fossil Invert., Mus. Coll. of 

 Surgeons. 4to, p. 5. 



