18 



Dr. Mantell on the Structure of the Belemnite. 



very thick and heavy, and invariably mineralized by calc spar : 

 the original structui-e was probably light and calcareous, like 

 that of the osselet of the Sepia. 



3. The Capsule, or sheath; a thin horny or testaceous case 

 which invested the osselet, and constituted the external envelope 

 of the receptacle ; it is seen partially covering the osselet at c, 

 fig. 1, and in section at e, /, fig. 2. This structure was for the 

 first time demonstrated in my memoir, ' Phil. Trans/ 1848. 



With the exception of obscure indications of a carbonaceous 

 fibrous structure between the dorsal processes, the above descrip- 



Fig. 3. 



tion comprehends all the facts re- 

 lating to the organization of the 



Belemnite with which we are at 



present acquainted : no soft parts, 



no traces of arms or tentacles, 



no vestiges of the eyes or man- 

 dibles, have been discovered. 

 The Belemnoteuthis. — From 



the extraordinarily perfect state in 



which some examples of the Be- 

 lemnoteuthis are met with, a brief 



description will suffice. Fig. 3 



(from a drawing with which Mr. 



Woodward of the British Museum 



has favoured me) exemplifies the 



essential parts of the structure of 



these Cepbalopods. The body is 



of an elongated form, with a pair 



of lateral fins, two large sessile 



eyes, eight uncinated arms, and a 



pair of armed tentacles ; each arm 



was furnished with from twenty to 



forty pairs of hooks, placed alter- 

 nately (fig. 4, 4). Like the Sepia 



it had a pigmental sac or ink-bag, 



which is generally filled with the 



inspissated seci*etion. The inferior 



part of the body is of a conical 



form, and contains a brown horny 



osselet, with a siphunculated phrag- 



mocone, which terminates in a 



rostrum of a fibrous structure 



(fig. 4, 5). The osselet of the 



a, the uncinated arms and tentacles ; b, remains of the head and eyes ; c, 

 the mantle, with indications of fins ; d, the pigmental sac or ink-bag ; 

 e, the osselet : the transverse lines indicate the septa of the phragmo- 

 cone, which is covered by a homy sheath or capsule ; /, the solid termi- 

 nal apex of the osselet. 



Belemnoteuthis antiquus 

 (i natural size, linear). 



