400 REVISION OF THE MONAXONID SPONGES, iii., 



SiDERODERMA ZITTELII. (Pl.XV., fig.6). 



The description of this sponge, which atttributes to it a unique 

 combination of the spicular characters, proves to be erroneous in 

 two vital particulars; the triehites, mentioned therein as forming 

 tlie cortical skeleton, are, in reality, small tylostyli, and chelae are 

 absent; also, there are no oxea present, though some of the prin- 

 cipal megaseleres are so narrowed at the base as closely to resemble 

 oxea. The general characters of the species are, in fact, distinctly 

 those of the genus Polymastia; and this, it would appear, was sub- 

 sequently discovered by Lendenfeld himself, for, among the frag- 

 ments received from the British Museum, there are two of this 

 species, one labelled actually Polymastia zittelii, the other bearing 

 the MS. name "Polymastia australis." There is only one specimen 

 (PI. XV., fig. 6) of the species in the Australian Museum, the claim 

 of which to be considered the type-specimen rests on the fact that 

 it is labelled, in Lendenfeld's handwriting, with the manuscript 

 name "Zittelia cligitata" the published equivalent of which is given 

 in the key-list as Sideroderma zittelii; and on the fact that, except 

 in the mentioned particulars and in some minor points in relation 

 to the dimensions of the spicules, it corresponds in every way 

 exactly with the description. One can only suppose that the chelae, 

 mentioned by Lendenfeld as occurring in the outer layer of the cor- 

 tex, were foreign; and the other errors are explicable on the sup- 

 position that the spicules were examined and measured only in situ. 



The species is nearly related to P. insidis Thiele(42), and per- 

 haps also to P. affinis Thiele(42), both of which it resembles in 

 this respect, namely, that the largest or fibre-forming spicules fre- 

 quently exhibit bulbous dilatations of their shaft. The following 

 brief account of the spiculation, taken along with Lendenfeld's 

 description of the external features and {vide infra) his figure of 

 the sponge (27, PI. ii., fig. 2), will be sufficient to enable one to 

 identify the species. 



/S'p?ci(7es.— These are: (1) Elongated, fusiform styli; forming 

 the fibres and also scattered between ; frequently polytylote ; 

 sharp-pointed at the apex; narrowing much (sometimes almost 

 pointed), at the base; with a maximum diameter of 22 /x, and a 



