R. W. H. ROW—REPORT ON THE SPONGES : CALCAREA, 209 
(ii.) Triradiates (Text-fig. 6, e).—Exactly similar triradiates were found 
in the dermal and gastral cortices and in the chamber-layer. They are 
described under the skeleton of the chamber-layer. The dermal cortex is. 
composed of a thin but very dense layer of these, filling up the interstices. 
between the subdermal quadriradiates. 
B. Gastral cortex. 
(i.) Quadriradiates (Text-fig. 6, d).— Very slender quadriradiates with 
an extremely small apical ray projecting into the gastral cavity. They are: 
sagittal, with the paired rays much longer than the basal and a very wide oral. 
angle. All the rays are straight and the facial are all equal in diameter. 
The apical ray is considerably more slender than the facial rays, and tapers 
nearly uniformly from base to apex. The facial rays are of the same 
diameter for the greater part of their length and have rounded ends. The 
paired rays vary from 0:25 to 0°28 mm. in length, the basal from 0°18 to: 
2 mm., all three facial rays having a diameter of 0-014 mm. ; the apical 
rays are about 0:05 mm. long, and 0-01 mm. in diameter. 
Gi.) Triradiates (Text-fig. 6, e).—Hxactly similar to those of the chamber-. 
layer, forming a thin but dense layer among the quadriradiates. 
C. Skeleton of the chamber-layer (Text-fig. 6, e, f). 
This part of the skeleton consists of a great mass of sagittal triradiates. 
scattered throughout the chamber-layer of the sponge, without orientation. 
There is easily distinguishable, in most spicules, a basal and two paired 
rays, by the great width of the oral angle. The basal ray is also usually 
not quite so long as the paired rays, but it may be equal to them in length 
or even longer than they are. All the rays are quite straight and of equal 
diameter almost up to the tip, which is somewhat rounded. 
There are also present in the chamber-layer, though not in the dermal or 
gastral cortex, a quantity of very small triradiates, which may very possibly 
be the incompletely developed specimens of ihe preceding. They are sagittal 
and have the paired rays always slightly longer than the basal. The 
thickness and form of the rays are the same as in the larger triradiates. 
Measurements of triradiates (in mm.). 
Basal ray. Oral rays. Diameter. 
ILarge triradiates ............ 0-2 to 0:28 0:25 to 0°30 0-014 
Small triradiates ............ O'14to 018 | 016 to 02 0-014 | 
A fragment of a single specimen was obtained at Suez. 
Distribution. Red Sea. 
