IJKLKMNIT.KS. 201 



dorsal region, supported laterally by two long, narrow, parallel, 

 calcareous plates (B. Puzosianus from the Oxford clay, fig'. 454). 

 Professor Huxley considers this difference between the pro- 

 ostraca of generic importance. 



G. The third kind of pro-ostracnm is exhibited by Ortliocera 

 elongata, De la Heche, tlic typo of the genus Xiphotenthis, Hux- 

 ley (fig. 460). It is calcareous, and is composed of concentric 

 lamella-, ouch of which consists of fibres disposed perpendicu- 

 larly to the plane of the lamella ; the phragmocone is very long 

 and narrow, and the guard cylindroidal. 



Professor Huxley suspects tlu.it a thoroughly well-preserved 

 specimen of Belemnoteutfyia will some day demonstrate the ex- 

 istence of a fourth kind of pro-ost racnm among the Belemnitidse. 



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

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

 either Belemnites. or Belemnoleuthis, or Plesioteuthis, or may 

 have belonged to the genus Celce-no" (HUXLEY.) 



The genus Belopeltix. Yoltz, was founded on the pro-ost raca 

 of Belemnites. 



The genus Actinocamax, Miller, was founded on the guards of 

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

 cayed, and thus presented no alveolar cavity. (WOODWARD.) 



Genus BELEMNITES, Lam. 



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'Orbign^y has presented the following scheme of sections and 

 subsections for dividing the large number of species of Belem- 

 nites ; they have been generally adopted. 

 26 



