﻿1^8 "ENDEAVOUK" SCIENTIFIC KESULTS. 



warty out-growths of the surface are probably incipient or 

 abortive branches; in fact, the longer ones ("8 mm. long") 

 mentioned by Lendenfeld are more correctly described as 

 young branches. This species is closely allied to, if not actually 

 identical with, Ridley's Myxilla arb ore seen s'^ which also 

 comes from Port Jackson. The spicules are asymmetrical 

 straight oxea, acanthostyles of two sizes and isochelae arcuatse. 

 The oxea, when more fully developed, show a very faint 

 sub-terminal constriction at both extremities, so that the end 

 portions appear somewhat lanceolate in shape. This feature 

 is usually more distinct at one extremity than the other, and is 

 often confined to one end. Sometimes one extremity is much 

 more rounded than the other, and then the spicule may appear 

 monactinal. In young spicules the asymmetry is more pro- 

 nounced, and the end which corresponds to the lanceolate 

 extremity of older spicules usually bears an elongated slender 

 tylosis. The spicules vary in length from about i6o to 285 fi, 

 though comparatively few exceed 220 ft ; the stoutest are 

 5 f< in diameter. The acanthostyles are conical and tapering, 

 and almost invariably curved ; the spines are densely crowded 

 on the basal end (the spicule appears in consequence somewhat 

 tylote), and decrease in abundance progressively from base to 

 tip ; more than one-third of the length distally, particularly in 

 the case of the larger spicules, may be free from spines. Their 

 length varies from about 85 to over 200 /i ; the largest 

 actually seen was 225 }i long. Individuals between 120 and 

 160 )i in length are extremely rare. The spicules accordingly 

 appear to conform to two sizes, the odd ones of intermediate 

 length being possibly stunted individuals of the larger kind. 

 Both kinds echinate the fibres. The largest acanthostyles are, 

 at most, 8 to 9 ji in diameter immediately above the base. The 

 chelae are abundant and measure 20 to 26 y. in length. Their 

 end parts are relatively small and the shaft may reach 4.5 /t 

 in thickness. A peculiar feature of the skeleton is the occur- 

 rence of elongated tufts of oxea, often standing off from the 

 main fibres as if they were short branches from them, which 

 have been left unpro\'ided with echinating spicules. 



Stylostichon conidosum, Whitelegge,! is sufficiently closely 

 related to Clathrissa arbuscula to be regarded as a variety 

 of it. The oxea are similar in shape to those of the latter, and 

 exhibit in some degree the same peculiarity. The sponge is 

 not encrusting in the proper sense of the word, but from an 

 encrusting base numerous miniature crumpled lamella.' with 

 conulated surface arise vertically. The oxea vary in length 

 from about 165 to 215 p ; the stoutest are 6 p in diameter. 



1 Whitelegge— Austr. Mus. Mem., iv., 10. 1907. p. 492. 



