210 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
Family PHARETRONIDA, Aittel. 
Subfamily Diarytina, Rauf. 
Genus KEBIRA,* n. g. 
Sponge composed of a single person with an apical osculam. The chamber- 
layer is covered over with a thick dermal cortex, in which occur numerous 
large oxea, longitudinally arranged. The spicular fibres are composed of 
triradiates, the paired rays of which are vestigial. The fibres lie radially 
disposed, or inclined but little to the radial direction, in the chamber-layer. 
The canal-system is leuconoid, with large subdermal cavities, inhalant and 
exhalant canals. 
This genus is of unusual interest not only as a living member of the family 
Pharetronidre, an almost wholly fossil group, but also on account of the 
presence of triradiates of very peculiar type. 
In the only other known living genus belonging to the subfamily Dialytine, 
Lelapia (2a), there also occur fibres of modified triradiates, in this case tuning- 
fork spicules, the paired rays being bent towards each other so that they 
come to lie parallel and close together, and almost in line with the basal 
ray. Thus the spicular fibre comes to be composed of spicules simulating 
oxea. 
In Kebira, however, the same result is obtained by a totally different 
method. Here, at first sight, the spicules of the fibres appear to be true oxea, 
but on more careful observation it is found that there is present on the inner 
(gastral) end of each, a small triangular head or swelling representing the two 
paired rays (text-fig..8, ¢). Although typically almost absent, yet there 
occasionally appear considerable rudiments of these paired rays, especially 
at the gastral end of the spicular fibre, where there are no surrounding 
spicules. All the paired rays are turned gastralwards, and the fibres run 
either radially, or very slightly inclined to the radial direction (PI. 20. fig. 9). 
It must be noted that where sufficient vestiges of the oral rays are 
present for their true shape and position to be made out, they are seen to be 
typically sagittal and to show no signs of turning inwards to form a tuning- 
fork spicule, so that it is not possible to derive them trom tuning-fork spicules 
by the loss of the paired rays. 
KEBIRA UTEOIDES, sp.n. (Pl. 20. figs. 8, 9.) 
Sponge of well defined flask-shape (Pl. 20. fig. 8) with a thick dermal cortex 
containing large longitudinally placed oxea. Dermal surface covered by a 
* The name is taken from the locality where it was obtained—Tella Tella Kebira. 
