REPTILIAN AGE. JURASSIC PERIOD. 125 



Porodragus, Montf. 1808, ib. 390. 



Belemnita, Fleming, Brit. Anim. 1828, 240. 



Notosiphiies, Duval-Johve, Belemu, 1841, 64. 



Gastrosiphites, DnvAL-JonvE, ib. 

 Etym. — Be'xs.mvov, a dart. 

 Examp. — Belemnites Puzosianus, D'Orbignt. 



Pen consisting of two parallel, nacreous, sword-snaped processes, extending for- 

 ward from the anterior dorso-lateral margins of the phragmocone. Guard elongated, 

 cylindrical, more or less clavate, or somewhat compressed; becoming very thin 

 anteriorly, where it is pierced by a deep conical cavity with entire margins, for the 

 reception of the phragmocone; solid and more or less pointed at the posterior 

 extremity. Phragmocone often terminating in a minute bulb at the apex ; septa 

 nearly horizontal, concave ; siphon contracted where it passes through the septa, 

 and somewhat expanded between them. 



Animal unknown. 



The guards of Belemnites, popularly called " thimderbolts," are the part most 

 frequently met with. They generally have a semi-translucent, somewhat horny 

 appearance, and a fibrous structure, the fibres radiating from a longitudinal, sub- 

 central line. It varies greatly in form and size in the different species and varieties, 

 as well as, apparently, in the two sexes. Sometimes it only extends about half an 

 inch beyond the phragmocone, whUe in other instances it attains a length of one 

 or two feet. It is readily distinguished from the guard of the allied genus Belem- 

 nitella by the absence of a slit down the anterior waU of the pierced end, and by 

 having no distinct vascular markings on the ventral side. It also wants the flattened 

 ridge always seen on the dorsal side of well preserved specimens of Eelemnitella. 



The genus has been divided into the following sections and subsections •} — 



Section 1. Acoeli, Bkohn. Without dorsal or ventral grooves. 



a. Acuarii, without lateral furrows, but often channelled at the extremity. (Lias and Neooomian). 

 Type. — B. acuarius. 



b. Clavati, with lateral furrows. 

 Type. — B. clavatus (Lias). 



Section 2. Gastrocoeli, D'Okeignt. = Notoslpbites, Duval. Ventral groove distinct. 



a. Canaliculati, no lateral furrows. (Oolites.) 

 Type. — B. canaliculatus. 



b. Hastati, lateral furrows distinct. (Upper Lias and Gault.) 

 Type. — B. hastatiis. 



Section 3. Notocceli, D'Orbignt. = Gastrosipllites, Duval. With a dorsal groove and furrow on each 

 side. 

 Type. — B. dilatatus (Neocomian). 



The great numbers of the guards of Belemnites often found imbedded together in 

 the same stratum indicate that these mollusks were gregarious in their habits, and 

 they are supposed to have preferred muddy bottoms. The genus made its appear- 

 ance near the beginning of the Liassic epoch, during which it seems to have attained 

 its greatest development. It contiaued, however, to exist untU about the middle 

 of the Cretaceous period. 



» Woodward's Man. Mol. p. f 4 



