﻿CLASSIFICATION. 



27 



basis to or towards the point. (No ink-bag ?) Species mostly confined to the 

 Middle Oolite, but rarely in Coral-Rag, and only peculiar kinds in the Inferior 

 Oolite ; two or three in Gault. 

 C. Fissae. — Basis with a deep short fissure, not extending backwards beyond the 

 alveolar region ; no furrows at the point. Confined to Cretaceous strata. 



D'Orbigny separates the third division of Bronn from other Bclemnites under the 

 title of Belemnitella ; for the others he forms five groups, characterised by peculiarities of 

 the rostrum or guard r 1 



1. Acuarii. — Rostrum more or less conical, often furrowed or wrinkled at the 



lower extremity, without ventral or lateral furrows in the anterior part. (Lias 

 and Oolites.) 



2. Canaliculati. — Rostrum elongate, lanceolate, or conical, provided below with 



a ventral canal occupying nearly the whole length ; no lateral furrows. (Inferior 

 Oolite and Great Oolite.) 



3. Hastati. — Rostrum elongate, commonly lanceolate, with lateral furrows on a part 



of the length, and an anterior ventral furrow, very distinct. (Lias, Oxfordian, 

 Corallian, Neocomian, and Gault.) 



4. Clavati. — Rostrum elongate, often clavate, with lateral furrows, but no anterior 



ventral furrow. (Lias.) 



5. Dilatati. — Rostrum compressed, often enlarged, with lateral furrows and a deep 



dorsal anterior groove. (Neocomian.) 



This author, from a study of recent Cephalopoda, was led to the supposition, and 

 finally, after researches among fossil groups, to the conviction, that in many Belemnites, 

 independently of age, the rostrum was longer or shorter in proportion to the alveolar axis, 

 according to sex, the males having a longer and the females a shorter guard. But with 

 advancing age, in some cases, the growth of the female guard restores, or nearly restores, 

 the equality. He regards the embryonic Belemnites as always composed of a sphericle 

 and a rostrum with a circular section. 



Mr. S. P. Woodward, in 1851, 2 presented a more practical view of the family of the 

 Belemnitidse than any previous British writer. The definitions of the family and its sub- 

 divisions are as under : 



Belemnitid.e. Shell consisting of a pen, terminating posteriorly in a chambered cone 

 (phragmocone) ; sometimes invested with a fibrous guard. The air-cells of the 

 phragmocone are connected by a slp/iuncle, close to the ventral side. 



' ' Terr. Jurassiques,' p. 73. 



2 ' Manual of the Mollusca,' p. 73. 



