BKKKMNITKS. 201 



dorsal region, su[)ported lateralh' bv two long, narrow, parallel, 

 calcareous plates {B. Puzo^iianua from the Oxford clay, fig. 454). 

 Professor Huxley considers this ditference between the pro- 

 ostraca of generic importance. 



G. The third kind of pro-ostracum is exliibiteH by Orthocerd 

 elongata. De la Beche. tlie type of the genus Xiphoteuthis, Hux- 

 ley (fig. 4(50). It is cak-a icons, and is composed of concentric 

 lamella\ eacli of whicli consists of fibres disposed perpendicu- 

 larly to tile plane of the lamella ; the phragniocone is very long 

 and narrow, and the guard cyliudroidal. 



Professor Huxley suspects that a thoroughly well-preserved 

 specimen of Belemnoteuthis will some day demonsti-ate the ex- 

 istence of a fourth kind of pro-ostracum among the Belemnitidse. 



" The Accmthofeuthes of Munster, so far as they are known 

 only by hooks and impressions of soft parts, may have been 

 either Belemnites, or Belemnoieuthis, or Plesioteuthw, or may 

 have belonged to the genus Celosno.''^ (Huxley.) 



The genus Belopelfis. Yoltz, was founded on the pro-ostraca 

 of Belemnites. 



The genus Actinocamaj:, Miller, was founded on the guards of 

 Belemnites and Belemnitella, the upper parts of which had de- 

 cayed, and thus presented no alveolar cavity. {Woor>WARP.) 



Genus BELEMNITES, Lain. 



These animals, supposed to have been gregarious, from the 

 number of their remains found in certain localities, were very 

 numerous in species, over 100 having been described from the 

 liassic and chalk formations of Europe, from the chalk of 

 Southern India, from the Jurassic of the Himalayas, etc. 



The phragmocone is very delicate, and its preservation is 

 usually due to the infiltration of calcareous spar into its chambers. 

 M. d'Orbigny supposes that the variation of the proportions of 

 the guard, as compared with the phragmocone, being sometimes 

 only a half-inch longer than the latter, and sometimes one or 

 two feet, depends partly' on age and sex. 



D'Orbigii}' has presented the following scheme of sections and 

 subsections for dividing the large number of species of Belem- 

 nites ; they have been generally adopted. 



