﻿.20 



BRITISH BELEMNITES. 



the undisturbed part, which is only |ths of an inch long. In the Oxford Museum is a portion 

 of the phragraocone of B. gigmteus, which has a length of 3^ inches, greater diameter 1\, 

 lesser If, and ten septa. If continued to the apex, its length would have been above 8 

 inches, the number of septa eighty or more, before becoming untraceable. The anterior 

 vaulted part of the phragmocone may be estimated as equal to the chambered part ; and 

 adding to this the probable extent of the guard, the total length of the shell would be not 

 less than 24 inches. 



This, however, is probably not the utmost length of Belemnites, such as those called 

 giganteus, Aalensis, and ettvpticus, in which sometimes the sparry guard behind the 

 phragmocone attains the length of a foot or more, and the total extent may have been 

 3 to 4 feet. 



Fifty septa occur in a specimen of B. paxillosus, in the Bristol collection, in a length 

 of 2*8 inches. 



The angle of inclination of the sides of the phragmocone is probably constant for the 

 same species of Belemnites, but it varies much in different specimens. Quenstedt gives a 

 section from Lyme Regis of a phragmocone with sides inclined at 8° 40 I have never 

 met with so slightly converging a cone in the Lias ; but among Mr. Moore's specimens 

 from Ilminster, usually referred to B. elongatus, is a cone with slopes meeting at 12°. 

 It is more common to find the angle above 20° and under 28° for all species in the Lias 

 and Oolites. I have a specimen measuring 32° ; unfortunately we cannot often refer these 

 phragmocones to their proper guards. 



The structure of the conotheca and of the transverse septa has not appeared the 

 same to every observer, partly because there may be some real differences in the shells of 

 different species, but more frequently from incomplete knowledge of the disguises induced 

 by laminae of bisulphide of iron and carbonate of lime attached to the real shell-structure. 

 To M. Voltz must again be awarded the praise of just observation in this matter. In 

 his ' Treatise on Belemnites,' an instructive figure is given, to show the difference between 

 the description of Miller and his own. This is copied in diag. 8, where M shows the 

 section according to Miller, V that according to Voltz. 



DIAGRAM 8. 

 V c a M 



/ e d c 



1 ' Cephalopoden,' t. 31, f. 1. 



