﻿460 DE. A. vaughajst on the fatjnal succession [Aug. 1908, 



the wall as well as at the centre, where they are fused together ; 

 in the cardinal region they are usually concave to the fossula 

 (although occasionally straight or very slightly convex). 



The constriction of the fossula is similar to that seen in the 

 D mutation of Zaphrentis Delanouei mentioned above, and the 

 fossula apparently lies in all cases on the concave side. 



Both theca and epitheca are abnormally thick, and intermediates 

 are buried in the theca. 



The early stage exhibits a parallel-sided fossula and distinct alar 

 breaks ; the curvature of the septa in the cardinal region is slightly 

 concave to the fossula. 



Although the general resemblance of the adult coral is certainly 

 to the gens of Z. Delanouei, the early stage does not strengthen 

 the evidence. 



A variant from P shows a remarkable thickening of the septa, 

 which brings them nearly into contact; in other respects it agrees 

 with the typical form. 



D. rusliianum is common in both Ds^ and D35, and the typical 

 form persists into P (L18c). The variant occurs in the Middle 

 Posidonomya-^edi^ (L 7). 



Other Densiphtllids . 



(a) The constricted D mutation of Z. Delanouei mentioned by 

 Mr. R. G. Carruthers, op. cit. p. 65. 



A specimen has been identified by Mr. Carruthers from P. The 

 mutation is, according to him, abundant in the Lower Limestone of 

 Scotland. 



(6) A new species of Densiphyllum, abundant at Bradbourne 



(Derbyshire), occurs in P. 

 A specimen has been discovered by Mr. Carruthers in the shales 

 above the Massif near Colne. 



Cyathaxonia. 



CrATHAXoNiA KUSHiANA, Yaughan. (PI. XLIX, fig. 9.) 

 *Eush paper ' p. 316 & pi. xxix, figs. 3, 3 a, & 3 6. 



The additional figure included in the present paper illustrates a 

 character of the septa which is not always obvious. 



The horizontal section shows a series of spine-like projections on 

 the sides of the septa, indicating the presence of interseptal dissepi- 

 ments either originally incomplete or subsequently, in great part, 

 destroyed. 



Further study of the species suggests that the projection of an 

 axial columella is merely due to the unequal resistance offered by 

 the several concentric shells of which the solid central cylinder is 

 built up, the middle shells being more easily removed. 



This species is common throughout the Cyatha.vonia-Beds (Bsa 

 and Dsb) and extends into P. 



