R. W. H. ROW—REPORT ON THE SPONGES : NON-CALCAREA. 307 
The colour in spirit is grey-black on the surface. When cut or broken 
the cortex appears grey and the choanosome a dark brownish grey. 
The ectosome (PI. 36. fig. 8) is differentiated into a distinct cortex, which 
varies in different parts of the specimen from 1'2 mm. to 1°4 mm. thick. In 
it occur the trienes, which are characteristic of the genus, and which in 
this species have undergone considerable malformation ; they lie quite irregu- 
larly, mixed up with the other spicules of the cortex. 
The main skeleton is arranged radially and consists of large bundles 
spicules. In the deeper parts of the sponge these bundles are very dense, 
the spicules composing them being very closely bound together; but near 
the outer surface they become spread out into a fairly loose brush, so that 
there is no unprotected part of the sponge surface, owing to the overlapping 
of the brushes. These brushes are chiefly composed of oxea, but anatrizenes 
and protrizenes also occur in them. The protrizenes are of considerable rarity, 
especially below the surface of the sponge. There is a special cortical 
skeleton consisting of a loose network of tangentially arranged oxea. These 
oxea are similar to those of the main skeleton, but do not reach quite so large 
a Size. 
In addition to the spicular bundles, the choanosome contains numbers of 
small oxea arranged very irregularly. The microscleres consist of sigmata, 
which occur in very large numbers throughout the choanosome, and rarely in 
the cortex. 
Spicules. 
A. Megascleres. 
(a) Protrizenes. 
The protrienes of this species are few in number and inconspicuous. 
They are nearly always found with the heads projecting from the sponge 
surface. They consist of a long slender shaft, which frequently does not lie 
quite regularly in the spicular bundle, and a head composed of three small 
cladi, which are sometimes unequal or somewhat irregular. The shaft varies 
from 2:0 mm. to 2°5 mm. in length, and is of the same diameter for the 
greater part of its length. For the last half-millimetre of its length it 
tapers very gradually to a fine point, the most distal portions of the rhabdome 
being almost hair-like. The maximum diameter of the rhabdome is 0:005 mm. 
The cladi are short and usually bluntly pointed ; they vary considerably in 
length, from 0:008 mm. to 0-02 mm., and their diameter at the base is equal 
to that of the rhabdome. The expanse of the head varies with the length of 
the rays, being usually approximately equal to their length. 
(@) Anatrizenes. 
The anatrienes are fairly numerous; a few of them have their heads pro- 
jecting from the surface of the sponge, but by far the larger number do not 
project. The heads of these non-projecting spicules almost invariably lie in 
