R. W. H. ROW—REPORT ON THE SPONGES : NON-CALCAREA. 345 
(ii.) Styles. (Text-fig. 20, A.) 
All the styles have spines on them, both at the surface and in the interior 
of the sponge, but both in amount of spinulation and in the length of the 
spines considerable variation occurs, the spicules nearest the surface being the 
most spiny, both in number and length of spine. Great variation also occurs 
in the length of the spicule, those in the interior of the sponge being much 
larger than those near the surface. Thus the largest spicules have the fewest 
spines and vice versd. The length of the styles varies from 0:1 mm. to 
0-24 mm. The diameter of the head, excluding spines, is on the average 
0:01 mm. 
B. Microscleres. 
G.) Chele. (Text-fig. 20, B.) 
The chelee are tridentate isochelee, and they occur chiefly on the sieve- 
membranes of the pore-areas and near the dermal surface of the sponge. 
They also occur in large numbers among the tylota forming the skeleton cf 
the pore-areas, and in the sphincter-membranes over the inhalant canals. 
They are all similar, and measure 0:02 mm. in length. The diameter of the 
shaft is 0°0036 mm. 
Gi.) Sigmata. (Text-fig. 20, C.) 
A few sigmata occur scattered about in the sponge. They are very slender, 
C-shaped or contort, and usually measure about 0°02 mm. in length. 
Locality. No locality is given, the bottles containing the specimens being 
merely labelled “ Sponge Trials 1.” 
Distribution. Red Sea. 
MYXILLA TENUISSIMA, n. sp. (Text-fig. 21.) 
There are three specimens of this species in the collection. Hach of them 
consists of very thin lamelle covering over a mass of calcareous and siliceous 
débris, but whether the sponge gathers these fragments together during its 
growth, it is impossible to say. In most parts the lamella covering the débris 
is extremely thin, often not exceeding 0°05 mm. in thickness, but occasionally, 
in crevices or between two pieces of débris not close together, the sponge may 
have a thickness of 0°3 mm. or even 0°5 mm. ‘The largest specimen forms 
an irregular mass 30 mm. x 25 mm. and is 25 mm. high. 
The surface is quite smooth and even, but under the microscope it can be 
seen to be very minutely hispid, owing to the projection from the surface of 
the points of the acanthosty li. 
The oscula and pores could not be made out. 
The colour of the specimens in spirit is a dense black, the pigment being 
contained in immense numbers of spherical or stellate cells, which oceur 
throughout the sponge. Frequently these pigment-cells are arranged in 
bands along the surface of the sponge, but the meaning of this could not be 
ascertained. 
