174 MANUAL OF THE “MOLLUSCA. 
of Southern India, and a few more in the 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 (siphunele), 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 the 
ventral 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. Acai (Bronn.), without dorsal or ventral grooves. 
Sub-section 1. Acwarii, without lateral furrows, but often 
channelled at the extreme point. 
Type, B. acuarius. 20 species. Lias—Neocomian. 
Sub-section 2. Clavati, with lateral furrows. 
Type, B. clayatus. 3 species. Lias. 
Section II. Gastrocatzi (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. Norocarz (D’Orb.), with a dorsal groove, 
and furrowed on each side. 
Type, B. dilatatus. 9 species. Neocomian. 
The belemnites appear to haye been gregarious, from the 
exceeding abundance of their remains in many localities, as in 
