THE STBOGTURE AND RELATIONS OF TUBIPORA. 571 



of importance is that " (Z») True tabulae are always present in 

 Syringopora, and in all the typical forms of the genus have 

 the character of a series of invaginated cones, which gives rise 

 centrally to an axial tube. In no specimens that I have ever 

 seen can there be recognised any similar series of funnel-shaped 

 tabulse in Tubipora. I cannot, in fact, recognise that any 

 true tabulae are present in Tubipora, so far as my own ob- 

 servations enable me to come to a conclusion on this point, and, 

 as already stated, I do not regard the axial tube of Syringo- 

 pora as being formed in the same way as the somewhat similar 

 looking structure in Tubipora, or as being really homologous 

 with it.'^ The description I have given in this paper of the 

 tabulae of Tubipora proves, 1 think, that the difference between 

 Syringopora and Tubipora is only one of degree and not one of 

 kind, and I cannot see that there is any evidence to prove that 

 the tabulae in the two are not homologous. There are perfectly 

 flat tabulae in Tubipora, as in some examples of Syringopora, 

 and there are cone-shaped tabulae fitting one into another as 

 in Syringopora (fig. 13, it). In fact, the only striking dif- 

 ference betweeu the two in respect to the tabulae is that in Tubi- 

 pora they are more sparsely scattered in the corallites, and are 

 more frequently of the form of axial tubes, open at both ends. 

 The third point of difference urged by Professor Nicholson is 

 that (c) "the corallites of Syringopora are provided with a 

 well-developed septal system, of which absolutely no traces can 

 be recognised in Tubipora. Moreover, the septa of Syringo- 

 pora are not mere marginal plicae, such as form the ' pseudo- 

 septa' of Heliopora, but they are in the shape of vertically- 

 arranged rows of spines, which may be well compared with the 

 septal spines of such undoubted Zoantharians as Porites.'^ In 

 answer to this the third and last objection of Professor 

 Nicholson I must point out that in some cases, as I have men- 

 tioned above, spicules do project into the corallites of Tubipora, 

 giving an appearance in transverse section exactly similar to the 

 individual septal spines of Syringopora, and that in many cases 

 the septal spines of Syringopora are exceedingly sparse and 

 reduced in size to a minimum, so that when a specimen of 



