370 ME. T. F. SIBLY ON THE CARBONIFEROUS [May I906, 



radial lamellae being equal to, or greater than, that of the primary- 

 septa. The lamellae are joined by a few concentric tabular 

 intersections. 



The primary septa, generally 30 to 32 in number, are stout and 

 well-spaced ; they do not extend to the outer wall. 



The secondary septa are short and thick, with club-shaped outer 

 ends ; they project inwards from the thick inner wall. This inner 

 wall, which constitutes a prominent feature, is formed partly by 

 the thickening of both series of septa, and also, in a considerable 

 degree, by the deposit of secondary matter. 



A septal break, though not always distinguishable, is often marked 

 by the stronger development of one of the secondary septa. 



The peripheral area, which is rarery preserved, is narrow and 

 variable, and is composed of large, compressed vesicles. It is not 

 radiated by the septa. 



The strong outer wall shows regular septal projections. 



Discussion. — The genus Carcinophyllum, as denned by James 

 Thomson, Proc. Phil. Soc. Glasgow, vol. xiv(1883) p. 455, possesses 

 all the essential characters of the form under description, differing 

 only in the more irregular structure of the central area. The 

 character of the central area, however, varies so much in different 

 sections of our species, that this point of difference is one of little 

 importance. 



Hesemblances and differences. — Care inop>hy Hum mendi- 

 pense, which characterizes the Lower Seminula-Zone in the Mendip 

 area, 1 resembles Carciaopliyllum Q, 1 which characterizes the Lower 

 DibunojoJtyllum-Zone, in all essential structural characters, and 

 the two forms are, undoubtedly, members of the same gens. 

 The important points of difference are : — (1) The much greater de- 

 velopment, in Carcinophyllum 6, of the peripheral vesicular zone. 

 (2) The strong development, in G. mendipense, of the thick, ring-like 

 inner wall. These differences of structure have an evolutionary 

 significance ; both the strong development of the vesicular zone, and 

 the type of septation, seen in Carcinophyllum d, indicate an approach 

 to the structural form typified by Lonsdalia. 



Cyathophylloid Clisiophyllids. 



(PL XXXI, figs. 5 a & 5 b) 



Small, cylindrical or cylindro-conical corals, which exhibit a 

 simple type of Clisiophylloid structure, in common with certain well- 

 marked Cyathophylloid characters, occur commonly in the Lower 

 Seminula-Zone of the Eastern Mendips. 3 



1 And in the Weston-super-Mare district also. The figured specimen was 

 obtained from this district. 



2 A. Vaughan, Quart. Journ. Geol. Soc. vol. Ixi (1905) p. 285 & pi. xxiv, 

 figs. 3-3 b. 



3 The earliest Clisiophyllids appear in the Syringofkyris-Zone. Their 

 characters are described by Dr. A. Vaughan, Quart. Journ. Geol. Soc. vol. Ixi 

 (1905) p. 286. 



