of Heliophyllum and Crepidophyllum: 51 
latter is distinguished fundamentally by the fact that the cen- 
tral portion of the tabulate area is enclosed by a distinct and 
separate wall, with which the primary septa become directly 
connected, the central space thus enclosed usually opening at 
one point to form a wide fossette bounded by two primary 
septa and containing two or three short septa. 
There is also a close relationship between Heliophyllum and 
Phillipsastrea, E. & H. The edges of the septa are occa- 
sionally denticulated in the latter genus in a manner appa- 
rently similar to that which obtains in Heliophyllum ; and there 
is also asmall central tabulate area. How far this resemblance 
is really founded upon identity of structure, I am not at this 
moment in a position to determine. At any rate, the genus 
Phillipsastrea is readily distinguished from Heliophyllum by 
the fact that the corallites of the former are wholly destitute 
of a proper wall, and become united by the confluence of 
septo-costal radii. 
It may be mentioned, finally, that there are some species at 
present referred to Acervularta (such as A. profunda, Hall, 
and A. Davidsoni, EK. & H., both from the Devonian forma- 
tion) in which the edges of the septa are denticulated, and 
their transverse section cross-banded, as in the genus Helio- 
phyllum. The more intimate structure of these forms, however, 
still awaits elucidation. 
So far as at present known, the genus Heliophyllum is ex- 
clusively restricted im its range to the Devonian formation, 
being known to occur in both the New and the Old World at 
this horizon. 
CrEPIDOPHYLLUM, Nich. & Thomson. 
Crepidophyllum, Nicholson and Thompson, Proc. Roy. Soc. Edinb. 
vol. ix, no, 95, p. 149. 
Corallum simple or compound—in the former case cylindrical 
or cono-cylindrical, in the latter case forming large fasciculate 
masses. Increase by lateral gemmation in the compound 
species. Epitheca complete, thin, with encircling strice and 
conspicuous annulations of growth. ‘T'abule not complete, but 
confined to a more or less extensively developed central area, 
the median portion of which is enveloped in a distinct accessory 
wall, and thus shut off from the rest. The median tabulate 
tube (fig. C) thus formed may be completely enclosed ; but 
more commonly it is open at one point, and the two extremi- 
ties of the horseshoe thus formed become directly continuous 
with two of the primary septa, which in this way include a 
wide septal fossula, within which are contained two or three 
short septa. The remainder of the primary ae are well 
