﻿278 DK. A. VAUGHAN ON THE TALiEONTOLOGICAL [May 1905, 



The figure illustrates a Lithostrotion characteristic of the Dibuno- 

 phyllum-Zoue ; this form resembles L. irregulare in its external 

 characters. 



L. irregulare and the members of the group of L. Portlocki show 

 a simple type of Clisiophyllid-structure. In a horizontal, section of 

 any of these forms, a few of the larger septa are seen to extend to 

 the thick columella, and they are crossed, in the central area, by two 

 or three tabular intersections. 



(4) Lonsdalia-like modification. 



The septa are inconspicuous near the wall, and there is a peri- 

 pheral area which is almost entirely vesicular. 



This type of structure is often partly developed in the typical 

 Lithostrotion Portlocki, but is especially characteristic of its variety, 

 L. ensifer, in which the walls themselves are feebly developed. 



Notes on the Species recorded in the Stratigraphical 

 Portion of this Paper. 



The Siphonodendron-Section. 



Corallites cylindrical ; growth dendroid. 



Lithosteoteon Martini, Edwards & Haime. 

 Here I include : — 



Lithostrotion Martini, Edwai'ds & Haime. ' Monogr. Brit. Foss. Cor.' 



pt. iii (1852) p. 197 & pi. xl, figs. 2-2g. 

 //. Phillipsi, Edwards & Haime, ibid. p. 201 & pi. xxxix, figs. 3-3 a. 

 Diphyphyllum lateseptatum, M'Coy, 'Brit. Palaeoz. Foss.' 1851, p. 88 & 



pi. iii c, figs. 10-10 b. 



The principal characters are as follows : — 



(1) The presence (except in D. lateseptatum) of a distinct 

 columella, not specially thickened. 



(2) Broad, nearly-flat tabulae. 



(3) The larger septa fall short of the columella, leaving a free 



space round it. 



(4) A small number of vesicles occurs in each interseptal space 



of the external area. 



There is great variation in : — 



(1) The diameter of the corallite, which varies, in specimens 



occurring at the same horizon, from 6 to 11 millimetres. 



(2) The grouping of the corallites. — The same mass is often, in 



parts, extremely flexuous and coalescent (when it is usually 

 named Lithostrotion Phillipsi) ; while, in other parts, the 

 corallites are almost parallel. 



(3) The number of vesicles in the interseptal spaces of the external 



area. — This depends, mainly, upon the size of the corallites; a 

 radial row of three or four vesicles may be regarded as the 

 usual type, but in the smaller forms this number may be 

 reduced to one only. 



