of Heliophyllum and Crepidophyllum. 49 
follows :—‘ Corallum simple, subturbinate. Septa well deve- 
loped, and giving origin laterally to lamellar prolongations, 
which are directed from the wall towards the centre, in an 
ascending and arched direction, so as to constitute irregular 
tabule in the central area. These lamellar prolongations are 
united circumferentially by vertical plates.” This defini- 
tion, however, is not only deficient in its details, but it is 
erroneous in the important point that the tabule of the central 
area are considered as formed by prolongations from the 
ascending dissepiments, whereas these structures, in reality, 
are wholly independent of one another. 
By Mr. Billings (Can. Journ. new ser. vol. iv. p. 124) the 
genus Heliophyllum is defined as follows :—‘‘ Corallum simple 
or aggregate; radiating septa well developed, obliquely 
striated on their sides by thin elevated ridges, which extend 
from the outer wall towards the centre. ‘These ridges are 
connected by numerous thin lamine which divide the spaces 
between the septa into small “sublenticular cells. The trans- 
verse diaphragms are thin, flexuous, and confined to the 
central portion of the coral.” This definition likewise omits 
many characters of importance; and the distinguished Cana- 
dian paleontologist is certainly in error in concluding that 
“the only difference between this genus and Cyathophyllum is 
the absence of the curved striae from the septa of the latter.” 
By Dybowski (Mon. der Zoanth. scler. rug. aus der Silur- 
formation &c. p. 83) the genus Heliophyllum is placed in a 
special family, Craspedophyllide, along with the two new 
genera Acanthophyllum and Craspedophyllum, the only 
characters assigned to the family being that there is no acces- 
sory wall, that the septa are complete, and that the sides of 
the septa are furnished with lateral outgrowths. As all these 
characters, however, might be predicated of other genera, it 
will hardly be possible to retain this family as it is at present 
constituted. Finally, a description of the generic characters 
of Heliophyllum, drawn chiefly from the beautiful silicified 
specimens of the Corniferous Limestone of North America, 
was published by the present writer (‘ Rep. on the Paleon- 
tology of Ontario,’ part i. p. 24, 1874). 
As regards the affinities of the genus Heliophyllum, it is 
_ certainly related to Cyathophyllum ; but the differences between 
these two genera are so many and so great that it cannot be 
said that the relationship is by any means a very close one. 
If we confine our attention to the simple and more typical 
members of the genus Cyathophyllum, the chief points of 
relationship with Heliophyllum are to be found in the pre- 
sence of an external vesicular area in both groups, in the 
Ann. & Mag. N. Hist. Ser. 5. Vol. 1. 
