CEPHALOPODA 93 



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

 taceous strata, from the lowest lias to the upper chalk. In its 

 ordinary imperfect state, it is a cylinder pointed at one 

 end (fig. 22, 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 laminoe of 

 growth. But even this " guard," which corresponds simply to 

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

 modifications 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 

 phragmocone, whilst in others it attains a length of ten 

 inches, and is tubular, as in B. acuarius. Some are fusiform, 

 others laterally 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 Belem- 

 nites of the chalk have been called Bclemnitellcc (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 orga- 

 nised 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 

 healed during life, are preserved in the British Museum. In 

 all perfect Belemnites, the alveolus is occupied by a fliragmo- 

 cone (fig. 22, p), with tender nacreous walls and septa, 

 terminating in a minute globular apex, and perforated by a 

 ventral siphuncle (fig. 22, i). The last chamber is rarely 

 preserved, and appears to have thinned off into a mere horny 

 sheath, with sometimes two pearly bands like knife-blades on 

 the dorsal side. It must have been sufficiently capacious to 



