sponges from South Australia. 127 



chiefly confined to tlie body and the small spicules to the 

 surface. Structure from without inwards consisting of a 

 thick, fibrous, tough, and smooth dermal layer, now of a dark 

 pinkish slate-colour, as above stated, charged with the small 

 or flesh-spicules, and contrasting strongly in colour with the 

 body-substance, which is much lighter and composed of the 

 body-spicules chiefly. Fragment about 3 in. in diameter. 

 Depth 20 fath. 



Group 28. T E T H Y I N A. 

 35. Tethya cranium^ var. australiensis. 



Massive, elliptical, convex, truncate, sessile (? cut off at 

 the base by the dredge). Consistence tough, firm. Colour 

 when fresh " yellow," now much the same, but faded. 

 Surface finely hispid. Vents small and numerous, here and 

 there among the pores of the reticulated dermis. Spicules 

 of four forms, viz. : — 1, skeletal, the body-spicule, an ex- 

 tremely long acerate, fusiform, with elongated and finely 

 pointed extremities, 1350 by 9-6000ths in., i. e. about ^ in. by 

 about l-600tli ; 2, zone-spicule or tetractinellid, arms simple, 

 extended fork-like, about 32-6000ths in. long, shaft a little 

 less than that of the body-spicule ; 3, a fine, minute, fusiform 

 acerate, microspined throughout, about 50-6000tlis in. long ; 

 4, bihamate or fibula, C- or S-shaped, about 4-6000ths in. 

 long. Structure from without inwards consisting of a thin 

 fibro-reticulate dermis, charged with the bihamate flesh- 

 spicule, in the interstices of which reticulation the pores are 

 situated, and through which the distal ends of the body-spicules 

 and the trifid ones of the tetractinellids project, which gives 

 the surface its fine, delicate, hispid character, followed in- 

 wardly by a compact structure, composed of bundles of the 

 skeletal acerates radiating from the centre towards the circum- 

 ference, held together by the sarcode, charged with the micro- 

 spined acerates and the bihamate flesh-spicules, and traversed 

 by the canals of the excretory systems. Size 4^ in. high in 

 the centre by 2^ x 1^ horizontally. 



Depth 20 fath. 



Ohs. The presence of the fine microspined acerate in great 

 abundance throughout the body-substance is the cliief distin- 

 guishing character of this variety. I saw no anchors (smaller 

 tetractinellids with recurved arms) ; but as their heads when 

 exposed are generally broken off (for they catch in every- 

 thing that they touch), it does not follow that they do not 

 form part of the spiculation, particularly as they are present 

 in most of the other species that have been described. 



