1104 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



becomes rather narrower. The individual is bare-mouthed ; the 

 outer and inner surfaces are slightly roughened by the cortical 

 and gastric triradiate spicules respectively ; the average thickness 

 of the wall does not exceed 0-6 mm. 



Skeleton : The skeleton consists of gastric triradiate, subgastric 

 triradiate, subdermal triradiate, dermal triradiate and acerate 

 s])icules. 



Gastric triradiate spicules sagittal, all rays in the same plane 

 and of the same diameter 15 mm. ; basal ray straight, tapering 

 from the base to a sharp point, length inconstant, usually one and 

 a half times as long as the lateral rays, often much shorter, lateral 

 rays curved outwards, cylindrical, either shai-ply or i-ather bluntly 

 pointed, each forming with basal ray an angle of about 110'*, 

 on an average 0*25 mm. long. Subgastric triradiate spicules^ 

 sagittal, all rays of the same diameter 0-02 mm. ; basal ray 

 straight, tapering from the base to a shaip point, usual length 

 0-38 to 0-45 nmi., lateral rays sharp pointed, curved, often 

 angularly bent in their middle or basal part rarely exceeding 

 0-275 mm. in length, forming with each other an angle varying 

 from 170° to 140°, and with the basal ray an angle varying from 

 100° to 120°. 



Subdermal triradiate spicules irregular ; all rays iisually of the 

 same thickness, 0-0 15 mm., but of different lengths, lying in the 

 same plane ; basal ray straight, tapering from the base to a sharp 

 point, rarely exceeding 0-1 mm. in length, occasionally rather 

 thinner than lateral rays, forming with each of these an angle of 

 about 120° ; lateral rays curved forwards, sharp pointed of 

 different lengths, the longer directed centripetally, reaching 

 0.35 mm. often, however, considerably shorter, scarcely longer 

 than the shorter ray, the length of which varies from 0"12 to 

 0-15 mm. 



Dermal triradiate spicules sagittal ; all rays of the same 

 diameter, 0-02 mm., usually sharp pointed; basal ray straight, 

 length inconsistent, not exceeding 0-425 mm. ; lateral rays curved, 

 each forming with basal ray an angle of about 120^*; average 

 length 0-25 mm. Acerate spicules usually spindle-shaped, often 



