178 



On a netc Sponge from Christmas Inland. 



p;iven by ]\Iincliin (Lankester's 'Treatise on Zoolofry,' Poii- 

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

 Dialytinfp, in my sense, included onh' one genus in Mincliin's 

 long list, viz. Lelapi'a, the whole of the vest of the genera in 

 that list coming under Lithoninas and Pharetroninse (see 

 below). 



Concerning the theory of the nature of the '' Pharetron 

 fibre," Rauff, in his great work' Paljeospongologie' (Pala^onto- 

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

 the fibre were simply in a{)position 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 spongo. 



riectroninia dean<>ii, sp. n. 



Fipr. 1. — Specimen incnistiiig rock. Nat. size. 



Fiir. 2. — Tlie same. X 6. 



Fig. 3. — Fide viev.- near edge of .sponge. X llo. 



Flu. 4. — Sm'face view. X To. 



Figs. o-S. — Small four-rayed spicules nf various sizes, 



Fig. 9. — Monaxon spicule. X 400. 



Fisr. 10.— Triaxon spicule, x 400. 



X 400. 



own investijiation of certain recont Pharetronid sponges 

 es me to the belief that Stcinmann's theory is the true 



j\ly ow 



inclines .„ — _ 



one. Among living Pharetrones we find, however, some 

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

 Avith Cf menti'd spicules (LithonniaO. A revised clas.-'ification 

 of Pliaretroncs, bn.«cd partly on tiiat of ^Minchin and partly 



