﻿STRUCTURE. 



21 



Miller supposed the transverse plate of the phragmocone to be composed of five 



parallel laminae, all bent forward to line the conotheca, which consisted of one thin plate 



only (M, in diag. 8). Voltz explains that the conotheca is formed of three lamina?; that 



it is bordered internally by only a short flange extended from the transverse plate; that 



it is inflected at the junction with this flange, the inflection being limited by two small 



incisions. The transverse plate (a, in diag. 8) is composed of several thin laminae, but is 



not so thick as the conotheca. Miller has not distinguished from the real substance of 



s 



the shell the thin lamina) of carbonate of lime (diag. 8, c) which often line internally the 

 conotheca and septa. My own observations agree in general with those of M. Voltz, but 

 it seems useful to describe the appearances presented in two or three easily procurable 

 species, which present some small differences. 



Diag. 9 represents the section along the dorsal face of three transverse septa abutting 

 on the conotheca. This enclosing shell is formed of three layers towards the opening, but 

 of two only towards the apex. Still nearer to the apex it is composed of one layer only, and 

 that finally ends in a porous or cellular plate, very like what can be traced on the limiting 

 texture of the spherule at or beyond the apex of the phragmocone. This Belemnite is in 

 the Oxford Museum, from the Lias of Lyme Regis. The septa are flanged, and, as it were, 

 bracketed where they meet the conotheca, and a small triangular interstice appears between 

 the bracket and the conotheca. 



In Belemnites vulgaris of Young and Bird, from the Upper Lias of Whitby, the septa 

 are apparently single plates — at least this appears to be the case in the hinder part of 

 the cone. 



DIAGRAM 9. 



In diag. 10, taken from another specimen in the Oxford Museum, from Lyme 



