BELEMNITID^. 4T 



tions of the guard, as compared with the phragmocoue, being 

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

 one or two feet, depends partly on age and sex. 



D'Orbigny has presented the following scheme of sections and 

 siibsections for dividing the large number of species of Belem- 

 nites ; they have been generally adopted. 



Section I. acceli (Bronn.), guard without dorsal or ventral 

 grooves. 



Subsection 1. Acuarii, without lateral furrows, but often 

 channeled at the extreme point. B. acuarius. 20 species. Lias 

 — Neocomian. 



Subsection 2. Clavati, with lateral furrows. B. clavatus. 

 3 species. Lias. (Includes the genera Pachyteuthis, Megateu- 

 this and Dactyloteuthis, Bayle.) 



Section II. gastrocceli (d'Orb.), guard with ventral groove 

 distinct. 



Subsection 1. Canaliculati, no lateral furrows. B. canalicu- 

 latus. 5 species. Inferior oolite — Great oolite. 



Subsection 2. Hastati, lateral furrows distinct. B. hastatus. 

 19 species. Upper lias — Grault. (Includes the genera Cylindro- 

 teuthis, Belemnopsis and Hibolites, Bajde.) 



Section III, notocceli (d'Orb.), guard with a dorsal groove, 

 and furrowed on each side. B. diloiatua. 9 species. Neocomian. 

 (Genus Duvalia, Bajde.) 



Heligerus, Dana, 1848. 



Distr. — 1 fossil species [H. Fuegiensis, Dana, xxix, 87), in 

 slate rock, Cape Horn. 



Shell like Belemnites, half-inch in diameter ; guard thick, sub- 

 cylindrical, fibrous ; phragmocone slender, terminating in a 

 fusiform spiral nucleus. 



Belemnitella, d'Orbigny, 1840. 



Syn. — Atractites, Link, 186Y. 



Distr. — 6 fossil species. Cretaceous ; N. Am. and Europe. B. 

 miicronata, Sowb. (xxviii, 70). 



Rostrum with a straight fissure on the ventral side of its 

 alveolar border; its surface with distinct vascular impressions. 

 Casts of the alveolus show that the phragmocone was chambered, 

 had a single dorsal ridge, and a ventral process entering the 

 fissure of the rostrum. 



XiPHOTEUTHis, Huxley, 1864. 

 Distr. — X elongata^ Beche (xxviii, 68). Liassic, England. 

 Rostrum and pro-ostracum calcareous, phragmocone very long 

 and narrow. 



