R. W. H. ROW—REPORT ON THE SPONGES : NON-CALCAREA. 349 
does not exceed 0:002 mm. at the thickest part of the shaft, which is of 
equal diameter for almost the whole of its length ; the head measures on the 
average 0:0025 mm. in diameter. A few spicules occur with oxeote or 
stylote ends. 
B. Microseleres. (Text-fig. 22, B.) 
The microscleres present in this species are toxa and are of extreme rarity, 
a single toxon being only found at long intervals during a careful search. 
That they acutally belong to the sponge is, however, shown by the facts 
that they are all exactly similar and that no other foreign bodies occur in 
the sponge. 
They are straight for most of their length, being sharply bowed in the 
centre, and they taper very gradually from the centre to each end. The 
actual ends are so delicate that it is a matter of considerable difficulty to 
ascertain the exact end to the spicule. They measure in length 0°06 mm., 
and are 0:0015 mm. wide in the centre. 
Locality. No definite locality is given for these specimens. 
Distribution. Red Sea. 
OPHLITASPONGIA (?) HORRIDA, n. sp. (PI. 40. fig. 26 ; Text-fig. 23.) 
The present species is very similar in its general character to the previous 
one, but differs from it in external form, in the character of the skeletal 
reticulation of spongin-fibre, and also in the shape of the toxa. 
The single specimen which represents this new species consists of a low, 
irregularly branching mass, creeping on coral and calcareous shells, from 
which arise at frequent intervals stout and short processes which frequently 
branch. The length of these processes between points of branching rarely 
exceeds 15 mm. The processes themselves and the branches into which 
they divide are stout and rather irregular in shape; they are usually about 
10 mm. in diameter, but are flattened and somewhat strap-shaped, in 
which case their greater diameter may be 15 mm. or 18 mm. and the 
shorter 5 mm. 
The surface of the sponge is smooth, but not glabrous, as it is echinated 
by the projecting ends of the spicules of the dermal skeleton. 
The oscula are numerous and very minute, not exceeding 0°2 mm. in 
diameter ; they are scattered irregularly over the whole surface of the 
sponge. 
The pores are scattered, very numerous, and small. 
The colour of the sponge is yellowish grey in spirit. 
The texture is firm, almost hard; it is somewhat compressible and very 
resilient. The sponge can be cut fairly easily, but torn with great difficulty. 
