1144 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



12:1; lateral rays smooth, tapering from base to sharp points ; 

 basal ray, if not shortened, also sharp pointed, if shortened, often 

 truncate, in both cases, however, of conical form ; size extremely 

 inconstant the length varying, in lateral rays, from 0-15 mm., to 

 1-8 mm. 



Snh -dermal Triradiate Spicules showing a rudimentary fourth 

 apical ray. 



Sub-dermal Triradiate Spicules of the convex surface. Sagittal, 

 all rays lying in the same plane, basal rays straight, tapering 

 from the base to a sharp point, ^-f , as thick as lateral rays and 

 either longer than these latter, not more than twice, or of the 

 same length, or even shorter, forming with each of them an angle 

 varying from 110° to 115° ; lateral rays either straight, or slightly 

 curved, average length 0*6 mm., the proportion between the 

 thickness and the length varying from 1 : 1 to 1 : 1 2. In the space 

 between the Oscula these triradiate spicules lie pretty regularly, 

 their corresponding rays being disposed more or less parallel one 

 to another, their basal ray turned to the closed end of the Sponge, 

 and the angle between the lateral rays towards the sharp margin 

 dividing the sieve-like surface from that bearing Oscula. Near 

 these latter as well as near the margin just mentioned, their 

 disposition becomes irregular, they lose their characteristic shape 

 presenting all possible transition forms to the sagittal triradiate 

 spicules of the sieve-like surface, and on the other hand, growing 

 smaller and becoming similar to the rectangular Triradiate ones 

 of the Oscular skeleton. 



Large Acerate Spicules of the convex surface lying in several 

 layers almost parallel to the surface, causing its smoothness and 

 silvery lustre. From length and comparative thickness extremely 

 variable, either spindle, club, or lance-shaped, or of quite irregular 

 outline, reaching 1 mm. in length, usually shorter, the proportion 

 between their length and thickness varying from 8:1 to 30:1. 



Oscula/r Acerate Spicules. Spindle or lance-shaped, usually 

 twenty-eight times as long as thick, rarely longer than 0"55 mm., 

 often considerably shorter. 



