16 



Dr. Mantell on the Structure of the Belemnite. 



The Belemnite. — In the specimen represented (fig. 1), and in 

 the diagram fig. 2, all the known parts 

 of the structure of the Belemnite are 

 displayed : but slight traces of any 

 portion of the organization of the ori- 

 ginal are preserved, except the sepio- 

 staire, which comprises an external 

 homy capsule, a calcareous osselet of 

 a fibrous structure, and an internal 

 chambered conical shell, termed the 

 phragmocone. 



1 . The Phragmocone (fig. 1 b, fig. 2^) 

 occupies the centre of the Belem- 

 nite : this is an inversely conical- 

 chambered shell, composed of a series 

 of shallow concave cells of a nacreous 

 substance, traversed by a siphunculus 

 or tube (fig. 2 c), which is situated on 

 the ventral region of the cone. The 

 phragmocone terminates distally in an 

 elongated apex, and enlarges towards 

 its basilar part, and two elongated flat 

 processes extend from the dorsal mar- 

 gin of the peristome or upper margin, 

 as shown in figs. 1 & 2 «, « : this struc- 

 ture was first detected in a specimen 

 discovered by my son near Trowbridge. 



The shape of the phragmocone, as 

 it appears when exposed by the re- 

 moval of the part next to be described, 

 is seen in fig. 2 d : the transverse lines 

 indicate the septa of the cells or cham- 

 bers ; the siphunculus which traverses 

 them is shown at c. 



Belemnites Puzosianus 

 {\ natural size, linear). 



a, a, the two basilar processes of the phragmocone ; b, the phragmocone, 

 much fractured and collapsed ; c, the rostrum or guard of the osselet, 

 containing within the upper part the distal portion of the phragmocone, 

 as seen in fig. 2. 



- 2. The Osselet (fig. 1 c, fig. 2h, i). — This body is in the form 

 of a very elongated inverted cone, and surrounds the phragmo- 

 cone throughout its entire length, as shown in section in fig. 2 : 

 the basilar or upper part is extremely thin, and blends with the 

 outer integument or capsule (fig. 2 b,b) : it rapidly increases in 

 thickness as it descends, and closely invests the phragmocone, 

 the delicate elongated apex of which is completely protected by 

 it (fig. 2fjff) : beneath this point it becomes solid, and in most 



