294. MARINE BIOLOGY OF THE SUDANESE RED SEA. 
(8) Anatriznes. (Text-fig. 1, B.) 
The anatrisnes are slender-shafted and but little longer than the ortho- 
trienes. The rhabdome is straight, conical, and very finely pointed ; it 
measures from 1:0 to 1°28 mm. in length, and 0-009 to 0°015 mm. in 
diameter. The cladi are abruptly recurved, so as to lie parallel with the 
shaft in their distal portions. They are rather short, not exceeding 0:1 mm. 
in length, and they are of an equal thickness with the rhabdome at their 
Junction with it. | 
The sagitta of the head is 0:06 mm. and the chord is 0:055 mm. 
(y) Oxea. (Text-fig. 1, C.) 
(i.) The oxea of the main skeleton are very 
sparse in the cortex, but occur in great numbers 
in the choanosome. They are straight, thickest in 
the centre, and gradually tapered to the ends, 
which are very finely pointed. The oxea vary 
very much in length, and specimens may be found 
measuring anything between 1:0 mm. and 2°6 mm. 
in length. The thickness is, however, fairly constant 
and averages 0:02 mm. 
(ii.) In addition to the large oxea, much smaller 
specimens, irregularly scattered through the sponge- 
body, can be found. These are apparently not young 
forms of the large oxea, but an entirely different 
spicule, similar to the somal oxea of Pilochrota varia- 
bilis, Wilson. They are extremely slender, and 
Fig. 1.—Pilochrota parva. almost raphide-like. They measure 0°25 to 0°37 mm. 
A,B,C, and E x 60; in length, and have a maximum thickness of about 
D x 1100. 8m 
B. Microscleres. 
The only microsclere which occurs is a small chiaster, with a very slight 
centrum and 6-10 rays. The diameter of an average specimen is 0:007 mm. 
The present species occupies an intermediate position between several 
previously described species. These are P. haeckeli, Sollas, P. pachydermata, 
Sollas, P. lendenfeldi, Sollas, and P. variabilis, Wilson. All these species 
differ from one another in shape, and also to some extent in their spicular 
measurements. Nor does P. parva agree with any of them with sufficient 
accuracy to be identified therewith, though any one of the spicules of P. parva 
can be almost exactly duplicated in one or other of the above species. 
For purposes of comparison I therefore give a table (p. 295) of these five 
species, with details of the spicular measurements &e. 
Locality. Suez. 
Instribution. Red Sea. 
