140 
THE AVONIAN OF THE AVON GORGE 
Cyathofhyllum. 
Corallum simple and cylindro-conical, or compound and 
massive. 
Septa numerous, close-set, radial, alternate in length and 
of nearly uniform thickness among themselves and throughout 
their length. The primary septa extend to the centre. 
A septal break is usually marked out by the shortening of 
one of the primary septa. This break is inconspicuous in a 
horizontal section, but is often represented, in the floor of the 
calyx, by a deep radial groove (‘ pseudofossula ’) ; especially is 
this the case when the floor is arched up into a broad central 
boss. 
The tabulae vary remarkably in the degree of their develop- 
ment : — 
The early Caninoid Cyatha^phylla (such as Cyath. (f> ) from the 
Syringothyris- zone have broad, close-set, flat tabulae. 
In Cyathophyllum Murchisoni, the tabulae are, for the most 
part, replaced by horizontal rows of vesicles, but true tabulae 
occur at intervals of every five or six rows of vesicles. 
In the Clisiophylloid Cyathophylla (such as Cyath. regium), 
from the Upper Dibunophyllum-zone, tabulae are typically 
absent, and are replaced by arched rows of small vesicles. 
The interseptal spaces are crowded with small, closely- 
packed vesicles, which are relatively scarce at the outer bound- 
ary of the central area. 
In the compound forms, the corallites are united by vesi- 
cular tissue and walls are only represented by a series of solid 
vertical rods, placed at intervals round each corallite. 
The essential characters of the Carboniferous Cyathophylla 
are 
(1) Very numerous, close-set septa, alternate in length, and 
not specially thickened at any point of their length. 
(2) The primary septa extend nearly or quite to the centre. 
(3) Vesicles are abundant from circumference to centre. 
Figures: Ed. and H. Plates 32 and 33 
