1108 A MONOGRAPH OP THE AUSTRALIAN SPONGES, 



Skeleton: The iubar quadriradiate spicules are regular, their 

 rays either tapering from the base to a sharp point, or of cylindrical 

 form with truncated ends ; in both cases the proportion between the 

 length and the thickness of the rays at their base remaining 

 the same 0*01, their length being 0-06 mm., their diameter 

 0*002 mm. These regular spicules of the radial tubes are connected 

 by all possible intermediate stages with sagittal and irregular 

 quadriradiate spicules supporting the inner surface. Constant as 

 to the thickness of their rays, only near to the Osculum exceeding 

 0-002 mm., the gastric quadriradiate spicules vary extremely with 

 regard to the comparative length of the rays, as well as with regard 

 to their form and their angles. The apical rays, which in the 

 tubar quadriradiates do not exceed the length of the facial rays, 

 and are often still shorter, grow much longer in the gastric 

 quadriradiate spicules, and near the Oscular part of the tube attain 

 0"18 mm. in length, and 0-005 mm. in diameter, the corresponding 

 facial rays rarely exceeding the length of 0-06 mm., the lateral 

 rays remaining of the same diameter, 0-005., the basal ray growing 

 rather thinner. 



Skeleton of the cortex. The triradiate and quadriradiate spicules 

 of the cortex are regular, their rays sharp-pointed, more or less 

 stout, the proportion between their length and thickness varying 

 from 6-1 to 12-1, With respect to their dimensions, the quadri- 

 radiate are connected with the triradiate spicules by intermediate 

 stages ; the length of the rays of the quadriradiate reaching 1 mm., 

 that of the rays of the triradiate not exceeding 0-6 mm. These 

 spicules lie apart from the centripetal ly directed apical ray of the 

 quadriradiate spicules, i)arallel to the outer surface, but the 

 direction of the basal rays is variable. 



Skeleton of the Oscidum. The skeleton of the border of the 

 Oscular circle consists exclusively of rectangular sagittal triradiate 

 spicules, marked by their horn-shaped lateral rays, lying parallel 

 to the line of the border. Their size is extremely inconstant, the 

 length of the rays from 0-05 to 0-25 mm., and the proportion 

 between the length and the thickness from 10-1 to 20-1. The 



