108 CARBONIFEROUS CORALS AND BRACHIOPODS 
Lithostrotion hasaltiforme, Phill., from which it chiefly 
differs in the smaller number of its septa and in its usually 
more open vesicular tissue, as well as, in the majority of 
specimens, by the smaller extension of its shorter septa ; 
but, as has been shown above, there is a considerable 
variation in all these respects amongst specimens derived 
from the same bed. 
From Lithostrotion aranea, McCoy, it differs chiefly in 
the thinness and non-prominence of its columella; for, 
though the broken section of the columella, often seen in 
the weathered calyx, is occasionally distinctly fusiform, 
no such appearance is ever exhibited in a horizontal sec- 
tion. Since, however, the Bristol specimens are clearly 
intermediate between these two species, it seems possible 
to regard L: aranea as itself only an extreme mutation of 
L. hasaltiforme. This species is one of the best known of 
all the Clifton corals. 
Lithostrotion Portlocki, Bronn ( N emato'phyllum clisi- 
oides, McCoy). 
There are several specimens in the collection of the 
typical columnar form. The polished horizontal sections 
exhibit the characteristically unequal, spidery septa and 
very open vesicular tissue, with scarcely any well defined 
inner wall ; diagonal of calices varying from 4 to 7 mm. 
These specimens have all been derived from the very top 
beds, and one is even labelled, “ 3rd bed below Fault.” 
Lithostrotion, Sp. 
Calices deep ; columella prominently projecting and stout. 
A horizontal section shows unequal calices varying from 
3 mm. to 7 mm. diagonal ; columella circular, often hazy, as if 
made up of very fine, spongy vesicular tissue ; twelve or 
