262 



"ENDEAVOUR" SCIENTIFIC RESULTS. 



This species is represented in the Australian Museum col- 

 lection by eight specimens, the largest of which measures 

 250 mm. in height by about the same in 

 breadth, and varies in thickness from 2 

 ^ mm. at the margin, where it is thinnest, 



to a maximum of '^.^ mm. Smaller 

 specimens are proportionately thinner. 

 The lamina is, frequently, irregularly 

 subdivided in a partite manner, and its 

 margin is sometimes lobate. In most 

 specimens, more or less distinct external 

 indications of intermittent growth are 

 noticeable ; Carter no doubt refers to 

 these when he describes the surface (of 

 PhakclUa papyracea) as "concentrically 

 lineated. " 



The skeleton is condensed along 

 radiating branched lines, and also, 

 owing to continued development of 

 spongin, greatly increases in density 

 with increase of age ; accordingly, sec- 

 tions taken from different portions of 

 the same specimen may differ consider- 

 ably in the pattern which they reveal. 

 In consequence of the linear condensa- 

 tions of the skeleton, the marginal re- 

 gion of the sponge lamina, if sufficiently 

 thin to be at all translucent, usually 

 shows to the naked eye an appearance 

 of subparallel venation — the "veins" 

 being, on an average, rather less than 

 I mm. apart. These veins are found to 

 be due to the presence of abundant 

 longitudinally disposed spicules, mostly 

 arranged in bundles. 



In the youngest, or marginal portions 

 of the sponge, before any readily notice- 

 able amount of spongin is developed, 

 the skeleton (except in proximity to the 

 surface) is an irregular "renieroid" 

 reticulation with triangular to polygonal 

 meshes, the sides of which are formed, 

 as a rule, each of a single spicule 

 enveloped in a minimum amount of 

 spongin. Towards the surface, how- 

 ever, excurrent pauciserial spongin-ensheathed lines of 

 somewhat plumosely arranged spicules (secondary fibres) 



Fig. 56 — O. tenuis. 

 a Principal styli. b 

 Auxiliary tylostylus. 

 (From a Port Phillip 

 specimeu.) 



