352 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
there arises a fourth short process, which lies parallel to the others throughout 
its length. 
The surface of the sponge is slightly irregular, being covered with low 
ridges or slight swellings. These prominences occur both on the basal 
undivided portion of the sponge and also on the digitiform processes. They 
are arranged quite irregularly, and entirely without relation to each other. 
The actual surface of the sponge is quite smooth and covered with a very 
delicate dermal membrane, which is not supported by a spicular skeleton. 
This dermal membrane has been rubbed off in many places, and here the 
surface appears finely reticulate with apertures between the meshes. 
The oscula are very numerous and occur all over the surface of the 
specimen, their arrangement being quite irregular. On the large processes 
as many as 20-25 oscula occur, and about the same number on the undivided 
basal portion of the sponge. They are fairly large, and measure 5 mm. 
or 6 mm. in diameter. An oscular sphincter membrane can be seen in some 
cases. The pores are small, very numerous, and scattered over the whole 
surface of the sponge. 
The texture of the sponge is like that of Kuspongia ; it is firm, very tough 
indeed, and difficult to cut, but easily compressible and also resilient. The 
sponge is also very soft to the touch. 
The colour is dark brown throughout the sponge in spirit. 
Skeleton arrangement. (PI. 37. fig. 15.) 
The skeleton consists of a very fine-meshed network of spicule-cored 
spongin-fibre, the meshes of which are of but little greater diameter than the 
the length of a spicule. 
Radial primary fibres can be distinguished, in which the spicules usually 
lie 3- to 4-serial, and these primary fibres occur regularly throughout 
the sponge about 0°12 to 0°2 mm. apart. They run straight from the centre 
to the circumference of the sponge, and occasionally divide into two. Occa- 
sionally smaller primary fibres arise from these, in which the spicules 
are only 2- or 3-serial, but as these separate from the parent fibre they 
become larger, and then take on the characters of the primary fibres 
themselves. 
Between these primary fibres there isan elaborate reticulation of secondary 
fibre, usually with the spicules lying uniserially, which forms an extremely 
regularly rectangular meshwork, the diameter of the meshes of which varies 
from 0:12 mm. to 0°16 mm. These fibres are but little less in diameter 
than the primary fibres, as the spongin is considerably more developed in 
comparison. 
A few spicules are scattered here and there outside the fibres. 
There is no special cortical skeleton. 
