SPONSIIDA. 475 



simply gre)'. A distinct cortical layer, containing the subcortical 

 crypts, and formed in adult specimens by the space between the 

 heads of the zone-spicules and those of the anchors, diameter about 

 •7 miUim. ; sarcode here of same consistency as in rest of sponge. 

 Sponge-sarcode belofr surface rather dark yellow-brown, rather 

 granular; that of surface (in weU-preserved specimens) reddish 

 brown, granular. 



Spicules : — (1) Zone-spicule, with long shaft tapering gradually 



from head to sharp point ; head composed of three bifid arms ; the 



proximal third of each arm projects forward at an angle of about 



120° to the shaft, and then bifurcates in a plane parallel to that of 



the surface of the sponge, so that the ultimate divisions are parallel 



with this surface ; the ultimate divisions taper gradually to sharp 



points from the point of bifurcation ; shaft about 3 miUim. long by 



•035 millim. in diameter ; total length of single arm "32 miUim., of 



proximal (simple) part •! millim. ; diameter of proximal part 



throughout ■028-032 millim., of base of ultimate divisions about 



the same. (2) Anchor, with long shaft tapering gradually from 



head to sharp point, and head composed of three arms tapering 



gradually to sharp points, curved backwards to form angles of about 



45° with shaft (the angles vary' slightly in different specimens) ; shaft 



about 2'1 millim. by '022 to -024 millim. ; expanse of arms •!! to 



•12 millim., diameter of arm at base about -02 millim. (3) Body 



acerate, long and slender, smooth, tapering gradually to sharp 



points from the centre ; size a,boufc 3 by '025 millim. (4) Plesh- 



spicule, composed of about 7 to 12 straight arms, radiating from a 



centre which does not show any perceptible inflation ; arms very 



slender (about -OOOS millim. in diameter), terminated by heads of 



about twice their own diameter ; spicule "01 to "013 miUim. in 



diameter across the arms : distributed generally in sarcode. 



Hah. Prince of "Wales Channel and West Island, Torres Straits, 

 7-9 fms. ; bottom sand and coral. Arafura Sea, off N.W. coast of 

 Australia, 32-36 fms. ; bottom sand, mud, and shells. 



This appears to be a small species, none of the specimens exceed- 

 iog 13 millim. in their longest diameter. It exhibits, as com- 

 pared with S. purpurea, a remarkable constancy in its form and 

 in the occurrence of a vent, and the spicules vary but slightly in 

 form and dimensions (the only variations observed are incorpo- 

 rated with the description above). In Torres Straits very few 

 specimens were obtained ; but in the Arafura Sea a considerable 

 number of small specimens occurred. SteUetta clavosa differs 

 from all nearly allied forms except S. tethyopsis, Carter, in the 

 bifurcation of the arms of the zone-spicule, and from the latter 

 species by the absence of " anchors " and of an external as distin- 

 guished from an internal form of stellate. The arms of the zone- 

 spicule are much longer in proportion to their thickness than in 

 Carter's species. 



• Parasite. In the superficial sarcode (probably just beneath the 

 ectoderm) of one specimeq occur a large number of a chain-like 

 Alga, resembling Nostoe, usually coiled, with very distinct cells. 



