1911.] Type of a New Family of Alcyonaria. 199 



From the evidence afforded by one of his letters, Nicholson appears to have 

 noticed the spicules, but he considered them to be adventitious. If they are 

 adventitious they belong to an Alcyonarian or possibly to a sponge that is 

 unknown. No such spicules as these have yet been described. The arrangement 

 of the spicules and their distribution in the walls of the tubes, however, give no 

 support to the view that they are adventitious. If they were adventitious in 

 the sense that the siliceous spicules of Polytrema and other Foraminifera are 

 adventitious, we should expect to find them irregularly arranged and more 

 numerous in some parts of the colony than in others. 



If they are the products of the Ceratopora itself, as I believe they are, then 

 we have another and most convincing proof that the genus is not related to 

 Heteropora and the Polyzoa. The presence of tuberculate spicules of calcium 

 carbonate suggests at once that Ceratopora is an Alcyonarian, and if it is true 

 that, at the surface, these long spicules are imbedded in a horny organic 

 substance, the condition is reminiscent of the walls of Glavularia (Hiclcsonia) 

 viridis, in which long slender tuberculate spicules are associated with a 

 number of horny fibres in the mesogloea. 



The principal difference between the spicules of Ceratopora and those of 

 Hicksonia is one of size. It is difficult to determine the exact length of any 

 one of the spicules of Ceratopora, as the part that is imbedded in the wall is 

 difficult to trace, but their total length cannot be more than 0*3 mm. and 

 their greatest diameter - 01 mm. The spicules of Hicksonia, on the other 

 hand, are 2 - 3 mm. in length by - 18 mm. in diameter. The very small size of 

 the spicules of Ceratopora is correlated with the very small size of the zooids 

 that formed them, and the small size of the zooids may be regarded as one of 

 the principal difficulties that may be felt in accepting the view that Ceratopora 

 is an Alcyonarian. 



The following list gives the diameter of the zooids of a few Alcyonaria for 



comparison with that of Ceratopora : — 



Hicksonia viridis 3 



Sarcodictyon catenata 1*5 



Heliopora ccerulea 075 



Xenia novce britannice - 8 



Ceratopora nicholsonii 0'2 



The small size of the tubes of Ceratopora is not a character that, by itself, 

 is sufficient to separate the genus from the Alcyonaria, aud, taking into con- 

 sideration all the other characters, the conclusion must be arrived at that the 

 affinities with the Alcyonaria are more pronounced than with any other group 

 of animals. 



