266 "ENDEAVOUR" SCIENTIFIC RESULTS. 



meshes zvith sides of a spicule's length. All the spicules 

 af ore-mentioned are principal styli; auxiliary tylostyli are 

 scattered in moderate number in the ground substance of 

 the interior, but become rather abundant in parts of the 

 outermost layer. In the youngest portions of the sponge 

 the skeleton differs from this mainly in absence of an 

 axial fibre-plexus. Megascleres : — (/.) Principal styli 

 curved, subcorneal to slightly fusiform, usually with a 

 slight sub-basal waist and slight basal knob, ranging in 

 le^igth from "j^ to 220 ]i, and in diameter up to 12 yi; [ii.) 

 straight auxiliary tylostyli, 140 to 240 }i in length, 2.5 }i 

 in niaxi)}iuni diameter. Microscleres absent. 



The single (spirit-preserved) specimen, the form of which 

 is sufficiently indicated by the figure (PI. xxxvi., fig. 2), 

 measures 90 mm. in height, inclusive of the stalk. The colour 

 is yellowish-grey ; the consistency moderately firm and tough. 

 Scattered over the surface at fairly close though irregular 

 intervals, are minute rounded openings mostly less than | mm. 

 in diameter. These are scarcely discernible on some parts of 

 the surface, very noticeable on others, being most pronounced 

 where apparently maceration has occurred ; it is therefore 

 probable that they are subdermal. No dermal membrane, 

 however, is observable ; this may be due to imperfect preserva- 

 tion, yet the membrane, if originally present, must have been 

 very thin. Towards the upper extremity of the branches a few- 

 larger openings (up to i mm. in diameter) occur, which are 

 possibly oscula. 



The appearance of the skeleton undergoes a marked change 

 with increase of age owing to the formation in the axial region 

 of the branches of a dense plexus of horny fibres. In this 

 respect the species is quite analogous to O. tenuis, to which 

 very probably it is related. The character of the skeleton in 

 the older portions of the sponge is so similar in the two 

 species, that what has been said in regard thereto in the case 

 of O. tenuis is also applicable in the present instance, except- 

 ing that here the extrafibral spicules of the axial region are 

 more abundant, the reticulation formed by the secondary and 

 their connecting fibres is less regular, the coring spicules of the 

 fibres are arranged in an axinelloid manner, echinating spi- 

 cules are plentiful, and auxiliary megascleres are rather 

 scarce. The formation of the axial plexus, however, appears 

 to be much longer delayed in the present species, being clearly 

 marked only in the stalk and the basal portions of the 

 branches. 



In the upper region of the branches, for a considerable por- 

 tion of their length, the skeleton is composed chiefly of 



