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THE AVONIAN OF THE AVON GORGE 
which is usually only imperfectly developed. The interspaces 
are filled with small, closely-packed vesicles which, by closer 
approximation at the inner boundary of the area, form a distinct 
inner-wall. 
The peripheral area, when present, is characterized by larger 
vesicles, and by the absence of conspicuous radiation ; it usually 
merges, quite continuously, into the external area. 
In the following descriptions of the best-known genera of the 
Clisiophyllids, attention is directed solely to diagnostic characters. 
Konincho'phyllum. 
Central area narrow and crossed by a mesial plate from 
which very few lamellae radiate outward. 
Septa alternate and fully developed, close-set and extending 
to the outer wall, uniform in thickness among themselves and 
throughout their length. 
This section is especially characteristic of Di in the South* 
Western Province, and is closely related to Lithostrotion. 
Acrophyllum. 
