174 MAKTTAL 01* THE MOLLTJSCA. 



of Soutliern India, and a few more in tlie Jurassic formation of 

 the Himalayas. The phragmocone of the belemnite, which, re- 

 presents the terminal appendix of the calamaries, is divided into 

 air-chambers, connected by a small tube [sipliunde), like the 

 shell of the pearly nautilus. It is exceedingly delicate, and 

 usually owes its preservation to the infiltration of calcareous 

 spar : specimens frequently occur in the lias, with the meniscus- 

 shaped casts of the air-chambers loose, like a pile of watch- 

 glasses. It is usually eccentric, its apex being nearest to tho 

 yentral side of the guard. The guard is very variable in its 

 proportions, being sometimes only half an inch longer than the 

 phragmocone, at others one or two feet in length. These 

 variations probably depend to some extent on age and sex ; 

 M. D'Orbigny believes that the shells of the males are always 

 (comparatively) long and slender ; those of the females are at 

 first short, but afterwards growing only at the points, they 

 become as long in proportion as the others. The guard always 

 exhibits (internally) concentric lines of growth ; in B. irregularis 

 its apex is hollow. Our knowledge of this genus now extends 

 to the form and proportions of the body, arms, the hooks, ink- 

 bag, one type of pro-ostracum and beak. The belemnites have 

 been divided into groups by the presence and position of furrows 

 on the surface of the guard. 



Section I. Acceli (Bronn.), without dorsal or ventral grooves. 



Sub-section 1. Acuarii, without lateral furrows, but often 

 channelled at the extreme point. 



Type, B. acuarius. 20 species. Lias — Neocomian. 

 Sub-section 2. Olavati, with lateral furrows. 

 Type, B. clavatus. 3 species. Lias. 



Section II. Gasteocceli (D'Orb.), ventral groove distinct. ■ 



Sub-section 1. Canaliculati, no lateral furrows. 

 Type, B. canaliculatus. 5 species. Inferior oolite — Great 

 oolite. 



Sub-section 2. Hastati, lateral furrows distinct. 

 Type, B. hastatus. 19 species. Upper lias — Gault. 



Section III. Notocceli (D'Orb.), with a dorsal groove, 

 and furrowed on each side. 



Type, B. dilatatus. 9 species. Neocomian. 

 The belemnites appear to have been gregarious, from tho 

 exceeding abundance of theii' remains in many localities, as in I 



