THE AVONIAN OF THE AVON GORGE 
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the base of each septum ; the branch from one septum unites, 
across the interseptal space, with a branch from the adjacent 
septum so as to form a dense wall. 
In Za'phrentis proper, this wall is in contact with the epithe- 
cal covering ; but in Caninia, this wall is separated from the 
epitheca by a broad ring of vesicles. Interseptal vesicles are only 
feebly developed. 
Zaj)hrentis. 
A 
f 
Horizontal section. 
/=‘Possula ’ 
ZJ=lateral breaks 
L.i= lateral groups 
A = antifossular group 
f 
Vertical section, showing 
cystoid tabulae and fossula. 
Generalized Diagrams. 
Corallum simple, conical and curved (‘ cornute ’) and usually 
small. Wall thick and composed of two distinct parts in 
close contact, the epitheca and the inner wall. 
Epitheca marked by concentric wrinkles and longitudinal 
rugae. 
Septa attached to the wall by thickened bases and tapering 
inward. 
The primary septa are long and extend nearly, or quite, to 
the centre of the corallum. 
The secondary septa are usually inconspicuous (except in 
the calyx-wall) and extend only a short distance from the 
wall. (They mark the junction of the septal lamellse which 
are formed by the forking of adjacent primary septa.) 
Septal breaks and groups: 
There are three main breaks in the septal sequence which 
divide the whole series of septa into three distinct groups. 
