228 Proceedings of the Royal Society 
connection with one another. In the latter case, on the contrary, 
the section of the corallite shows a number of irregularly concentric 
lines, marking the cut edges of the ensheathing tabulae, the outer 
of these lines being in connection (as a rule) with the wall of the 
theca, while the innermost encloses the cavity of the axial tube. 
While the above are the real or supposed points of resemblance 
between Tubipora and Syringopora, there are the following very 
important differences between the two genera to he observed. 
(a.) In the first place, there is the very important and remark- 
able difference in the minute structure of the calcareous skeleton in 
the two types in question. In Tubipora the corallum is made up of 
fused calcareous spicules, which are so disposed as to give rise to a 
universally distributed system of minute canaliculi or tubuli, which 
open on both the outer and inner surfaces of the skeleton by well- 
marked apertures. The size of these tubuli is comparatively so 
great that it is quite impossible that their presence could he over- 
looked in thin sections of Syringopora , if they really existed in this 
genus. On the other hand, the skeleton of Syringopora, as regards 
its minute structure, is quite compact, and shows no signs whatever 
either of being penetrated by a system of tubuli, or of being formed 
by the fusion of ectodermal spicules. 
(b.) True tabulae are always present in Syringopora, and, in all the 
typical forms of the genus, have the character of a series of invagi- 
nated cones, which give rise centrally to an axial tube. In no 
specimens that I have ever seen, can there he recognised any 
similar series of funnel-shaped tabulae in Tubipora. I cannot, in 
fact, recognise that any true tabulae are present in Tubipora , so far 
as my own observations enable me to come to a conclusion on this 
point, and, as already stated, I do not regard the axial tube of 
Syringopora as being formed in the same way as the somewhat 
similar-looking structure in Tubipora, or as really being homologous 
with it. 
(c.) The corallites of Syringopora are provided with a well- 
developed septal system, of which absolutely no traces can he 
recognised in Tubipora. Moreover, the septa of Syringopora are 
not mere marginal plicae, such as form the “ pseudosepta ” of 
Heliopora, hut they are in the shape of vertically-arranged rows of 
spines which may he well compared with the septal spines of such 
