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THE AVONIAN OF THE AVON GORGE 
This genus is usually simple, but compound forms have been 
found. 
Central area oval and with a well-defined boundary ; mesial 
plate short, and entirely surrounded by a reticulate network ; 
lamellae approximately equal in number to the septa. 
Primary septa, usually 33 in number, well spaced and 
thickened, especially at the inner wall. 
Secondary septa short and stout, and also thickened at the 
inner wall. 
Peripheral area purely vesicular, the vesicles being large. 
(In weathered specimens of this coral, the peripheral area is 
very liable to destruction on account of its loose structure.) 
An external area is practically undeveloped. 
This genus ranges from Si to Di in the South-western 
Province. 
The essential distinction from Lonsdalia lies in the struc- 
ture of the inner wall. In certain of the earliest forms 
from Si, the inner wall is produced by the coalition of the 
thickened ends of the two series of septa, a type of structure 
which indicates convergence with such a form as Zaphrentis 
aff. cornucopiw. 
In the later forms from S 2 and Di, the septa are more spaced 
and the inner wall is formed by the forking of the septa at 
their base and by the union of the branches from two adjacent 
septa, a type of structure which is characteristic of Caninia. 
It is not, however, unusual to find, in specimens from Di 
that the inner wall is weakly vesicular and such specimens 
exhibit an approach towards the structure of Lonsdalia. 
It is possible that Lonsdalia is directly derived from Carcino- 
phyllum, but the evidence is, as yet, very incomplete. 
Already in Di, Carcinophyllum exhibits old age characters, 
as shown by the excessive development of the peripheral 
vesicular area, and by the growth of roots (characters which are 
also well shown in Lonsdalia). 
