210 SIDERODEKMA. 



sand-grains. The fibres measure 0-3 millim. in thickness, and the polygonal 

 or square meshes ot' the network are 1*2 millim. wide. 



Geographical Distribution. — East coast of Australia : Port Jackson, 

 N. S.W. {Ramsay, Lendenfeld). 



Familia DESMACIDONID^. 



Cornacuspongia3 with a supporting skeleton composed of spicii- 

 liferous, often ecliinated fibres. Generally with chelae in the 

 ground-substance. If chelae are absent, the fibres are echinated 

 by projecting spicules. 



8ubfamilia ESPEEELLIN^. 

 Fibres not echinated. 



Genus SIDERODERMA. 



Desmacidonidae with mammiform projections and a dense ex- 

 ternal rind of closely packed tangentially disposed megasclera. 

 Soft in the interior. Megasclera smooth. Microsclera isochelae, 

 trichites, and (usually) sigmata. 



Sideroderma navicelligerum, Eidley & Dendy. 

 (Plate II. fig-. 2.) 



Sideroderma navicelligerum, S. O. Ilidley and A. Dendy, " Preliminary Iveport 

 on the Monaxonida collected by H.M.S. Challenger," Annals and Maga- 

 zine of Natural History, sex\ 5, vol. xviii. p. 348 (1886). 



Hemispherical, sessile sponges, with a hard and dense rind about 1 millim. 

 thick, composed of closely packed tylota. The surface is covered with nume- 

 rous papillae, some of which bear terminal vents. Colour in spirit pale 

 yellow. 



Spicules : — (1) Tylota with a long cylindrical shaft and an oval head at each 

 end, length 0-28-0-595 millim., diameter in middle of shaft 0-0063-0-0126 

 millim. ; (2) very fine long trichites, in bundles measuring about 0-45 by 0-17 

 milhm. ; (3) sigmata : («) large, measuring 0-06 by 0*0047 millim., and {h) 

 smaD, measuring 0-0189 by 0-015 millim. ; (4) tridentate isochelae, length 

 0-019 millim. ; (5) A'ery minute isochelse of peculiar form, shaft much expanded 

 laterally all along, so as to become oval and flattened, and notched in front in 



