THE AVONIAN OP THE AVON GORGE 137 
A horizontal section exhibits three areas : — 
(1) A central area, practically free from septa, which is 
occupied by the tabulae. 
(2) A medial area, radiated by subequal thickened primary 
septa which fork at their bases to form a thick inner 
wall, as above explained. 
(Short thickened secondary septa are usually, but not in- 
variably, developed.) 
(3) An outer area which is built up of closely-packed vesicles, 
and is imperfectly radiated by thin prolongations of 
both series of septa. 
Tabulae broad and flat across the central and medial areas, 
but bent downward at the inner wall. 
(In the medial area, the septa are attached to the upper 
surfaces of the tabulae.) 
The septal break is marked out by the shortening of one of 
the primary septa and by the arching of the adjacent septa 
round it. 
The fossula is a deep depression of each tabula at the septal 
break ; it is recognized in a horizontal section by a series of 
arched tabular intersections. 
(The septa on the fossular side of the corallum are often 
remarkably thickened.) 
The essential characters of Caninia are : — 
(1) The deep fossular depression and marked septal break. 
(2) The practically-radial symmetry, due to the suppression 
of a Za'phrentis type of grouping. 
(3) The envelope of closely-packed vesicles. 
(4) The thickened septa and the construction of the inner 
wall. 
(5) The broad flat tabulae. 
Figures: Ed. and H. Plate 35 
