146 
THE xiVONtAN OF THE AVON GORGE 
strongly differentiated and cuspidate ; vesicles are closely- 
packed and an inner wall is very distinctly marked out. 
This section must be regarded as the type genus of the 
Clisiophyllids. 
Central area surrounded by a distinct wall and crowded with 
minute vesicles. (So strongly is the bounding wall of this area 
developed that, in weathered specimens, the central portion 
often stands out as a distinct tube.) In the very centre of the 
area the vesicles are comparatively large, whereas, near the 
circumference, they are extremely minute. Very numerous 
thin radii extend from the circumference inward for a short 
distance. 
The medial and external areas resemble those of Konincko- 
phyllum. 
[N.B. — Aulofhyllum is separated from Cydo'phyllum by the 
presence of flat tabulae in the middle of the central area^ 
but, since the vesicles of a Cydo'phyllum always become broad 
and flat at the very centre of the coral, it seems doubtful 
whether the distinction can be usefully maintained.] 
The genesis of this section is not yet clearly understood, but 
it may be pointed out that Cydophyllum pachye'ndothecum could 
be derived from Cyathophyllum Murchiso'uihj enclosure of 
the inner vesicular mass within a special tube (involving the 
inclusion also of the inner portions of the septa). 
