5G2 SYDNEY J. HICKSON. 



but many more could have been figured showing features quite 

 as complicated as this. 



Before leaving the tabulae, I may mention that at first I 

 had some difficulty in determining the exact shapes of the 

 tabulae. They are frequently exceedingly delicate, crumbling 

 at the slightest touch or blown away by the slightest breath. 

 The only satisfactory way of exposing them is to carefully file 

 away the wall of the corallite until a small hole is formed, and 

 then, with a fine pair of forceps, break away the parts of the 

 wall which have been thinned by the filing process. 



When the corallites or platforms of Tubipora are examined 

 with a hand lens, the coral is seen to be covered by numerous 

 round holes (fig. 2), and thin transverse sections reveal the fact 

 that these holes completely penetrate through the walls of the 

 corallites and the platforms. These perforations have already 

 been described and figured by Professor Nicholson (20, fig. 2), 

 and, as he points out, they are not always in the form of simple 

 tubuli, but are very often branched. The examination of thin 

 sections reveals the fact that the corallites are built up of a 

 number of spicules, which are so firmly bound together that it 

 is impossible to separate them without injury. Both Professor 

 Wright, who first discovered this, the true nature of the skeleton, 

 and Professor Nicholson, speak of the spicules as being " fused" 

 together. I think the employment of this word is likely to 

 lead to misunderstanding. The spicules are not really fused 

 together, but firmly bound together by means of minute serra- 

 tions fitting into minute serrations, just like the membrane 

 bones of the skull. The sutures between the spicules can 

 always be seen (fig. 9, Sp.), and I have no evidence at com- 

 mand to prove that they are ever obliterated. In the walls of 

 the corallites the sutures have a tendency to run across — that 

 is to say, in a direction parallel with radii drawn from the 

 centre of the corallite, and similarly, the longest axes of the 

 spicules are usually disposed in the same direction. This fact 

 is of some importance, as occasionally individual spicules will 

 project out radially into the cavity of the corallite in a manner 

 exactly similar to the so-called "septa" of Syringopora. 



