Rk. W. H. ROW—REPORT ON THE SPONGES : NON-CALCAREA. 313 
off, so that the trieene head is not present, yet they can always be distin- 
euished from the oxea by the much more slender rhabdome. Both anatrizenes 
and protrieenes occur in this species, and both kinds occur with their heads 
both projecting from and buried in the sponge. Of those projecting from 
the sponge it is impossible to determine the proportions in which the two 
kinds of spicules occur, owing to the breaking off of the trisene-heads referred 
to above ; but of those which still retain their cladi, the anatrizenes are much 
the more plentiful, both outside and inside the sponge, 
Fig. 8.—Chrotella ibis. Trienes, x 30. 
The two spicules on the top line are the normal type of spicule; those in the 
second row are abnormal forms, the heads of which protruded from the 
sponge surface; the third row contains similar abnormal forms which 
were entirely embedded in the sponge tissue. 
The most characteristic feature of these spicules is the constant malforma- 
tion of the heads, in both kinds, so that the cladi are frequently reduced in 
number, and those that are present of unequal length, or the whole head may 
be reduced to a knob. In addition extra cladi may occur on the rhabdome, 
as many as five such being seen in one case; spicules bearing these extra 
cladi have not, however, been seen outside the sponge. Both these cladi and 
