178 



On a neia Sponge from Christmas Island. 



given Ly Mincliin (Lankester's 'Treatise on Zoology,' Pori- 

 feia. p. 110) ; but my statement was partly incorrect, for the 

 Dialytina*, in my sense, included only one genus in Minchin's 

 long list, viz. LeJapia, the whole of the rest of the genera in 

 that list coming under Lithonin^ and Pharetroninse (see 

 below) . 



Concerning the theory of the nature of the '' Pharetron 

 fibre," Kauff, in his great work ' Palseospongologle ' (Palseonto- 

 graphica, Bd. 40), expresses the belief that the spicules of 

 the fibre were simply in apposition in the living sponge, and 

 that they have been cemented into solid fibres during the 

 process of fossilization. Steinmann (' Palseontologie,' ed. 2, 

 1907) considers that the spicules have been joined together 

 by a cement formed by the living sponge. 



riectroninia deansii, sp. n. 



Fig. ] . — Specimen incrusting rock. Nat. size. 



Fig. 2. — The same. X 6, 



Fig. 3. — Side view near edge of sponge. X 115. 



Fig. 4. — Surface view. X 75. 



Figs. 5-8. — Small four-rayed spicules of various sizes. X 400. 



Fig. 9. — Monaxon spicule. X 400. 



Fig. 10.— Trlaxon spicule. X 400. 



My own investigation of certain recent Pharetronid sponges 

 inclines me to the belief that Steinmann's theory is the true 

 one. Among living Pharetrones we find, however, some 

 with spicules uncemented {Lelapia, Kehira), and others again 

 with cemented spicules (Litiionma?). A revised classification 

 of Pharetrones, based partly on that of Minchin ai:d partly 



