398 
DR. MANTELL ON THE BELEMNITE. 
Fig. 5. The rostrum of the osselet of Belemnites Puzosianus from the Oxford Clay, 
Trowbridge, Wilts. In this specimen the upper part of the guard is re- 
moved and exposes the distal extremity of the phragmocone lying in its 
natural position in the alveolus. The ventral aspect is delineated to show 
the form and situation of the sulcus or groove (the characteristic of this 
species) in that region : the siphunculus is on the front of the phragmocone 
in this view. 
The several parts represented in the above figures are indicated as follow : — 
a, a. The pair of elongated processes of the phragmocone. 
h. Osselet, rostrum, or guard. 
P. The upward extension of the expanded osselet. 
c. c. Siphuncle. 
d. d. The phragmocone. 
e. Section of the capsule or outer investment of the osselet. 
f. The apical or distal termination of the phragmocone. 
g. The alveolus or hollow in the rostrum in which the end of the phrag- 
mocone is situated. 
h. Vertical section of the guard, showing its fibrous and radiated structure. 
i. Ventral aspect. 
h. Ventral sulcus or groove. 
1. Section of the capsule investing the guard. 
Fig. 6. Transverse section of a fragment from the upper part of the receptacle of the 
Belemnite near the base of the process ; magnified eight diameters. 
In this thin pellicle are seen, a. the Capsule ; h. the radiated fibrous structure 
of the osselet distinctly visible, though taken several inches from above the 
line which is usually regarded as the termination of the spathose osselet; 
c. the shell of the phragmocone. 
Fig. 7- The apical or distal end of the phragmocone of the Belemnoteuthis, showing 
the ventral aspect, and the pair of ridges : natural size. 
7®. A transverse section of the same, displaying the internal radiated struc- 
ture of the phragmocone and its solid apex : magnified four diameters. 
* * The two ventral ridges. This specimen is in my collection. 
Figs. 9, 10. The apical portion of the osselet of the Belemnoteuthis, exposing the 
alveolus, or cavity occupied by the apex of the chambered cone, filled 
with spar, and surrounded by the dense, fibrous, radiated investment, 
analogous to that of the guard of the true Belemnite : the figures are 
magnified four diameters. 
PLATE XXX. 
A Belemnite from the Oxford Clay of Wiltshire, showing the pair of dorsal pro- 
cesses in their natural position : size of the original. 
