CARBONIFEKOUS CORALS AND BRACHIOPODS 
95 
II. DESCRIPTION OF THE CORALS. 
Alveolites. 
Alveolites septosa, Flem. (including A. depressa, Flem. 
= A. capillaris, PhilL). 
Corallum hemispherical, cylindrospherical, etc, ; diameter 
of corallites varying from *35 mm. to more than -5 mm. 
No sharp distinction can possibly be drawn between those 
forms in which the corallites are very narrow, the tabulae 
very distinct, close and regularly spaced (depressa section), 
and the forms with larger corallites and with fewer and less 
regularly spaced tabulae (septosa section). The gradation 
in diameter is perfectly continuous, so that specimens 
occur having corallites of every intermediate dimension. 
Again, the narrower corallites in a specimen of the typical 
septosa section are usually quite as closely and regularly 
tabulate as the corallites of the typical depressa type. 
All the individuals, without regard to dimensions, usually 
exhibit, on their outer surface, certain scattered patches 
in which the tube openings are of larger size, and these 
patches are often a little raised above the general surface. 
There are in the collection very numerous specimens, 
both polished and unpolished, v/hich illustrate excellently 
the complete transition between the two mutations. 
All the specimens have been derived from the uppermost 
section of the Carboniferous Limestone and from both the 
lower and upper divisions of that section (e.g. bottom of 
New Zig Zag, Boiler Bed, behind Colonnade and correspond- 
ing positions on the south side of the Avon). 
Alveolites Eiheridgei, Thomson. 
1. This species is undoubtedly represented by a polished 
section which exhibits elongated, narrow spaces, bounded by 
thickened walls ; the contiguous spaces being separated 
by short thickened transverse partitions. Owing to the 
continuity of the long walls (the elongated spaces being 
