300 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
The skeleton consists chiefly of bundles of spicules, arranged more or less 
radially ; but large numbers of spicules oceur scattered through the sponge, 
and not bound up into bundles. The spicular bundles are fairly large, 
averaging 0°3 mm. in diameter, and in the deeper parts of the sponge are 
closely bound together. Dermally, however, they become somewhat plumose 
in character, and sometimes lose the appearance of fibres. The megascleres 
consist wholly of diactinal oxea of one kind; and the oxea of the spicular 
fibres cannot be distinguished either from those scattered about in the 
choanosome, or from those of the dermal tangential skeleton. Only one sort 
of aster is present, a minute euoxyaster. 
Spicules. (Text-fig. 3.) 
A. Megascleres. (Text-fig. 3, A.) 
(i.) The somal oxea are typically somewhat curved, sometimes having a more 
or less definite angle in the middle, more frequently gradually throughout 
their length. They are thickest in the middle and gradually taper towards 
the ends. All sizes can be found, from minute raphide-like forms to the 
full-grown specimens, which measure 0°9 mm. to 1-1 mm. in length by 
‘0:025 mm. to 0:04 mm. in diameter at the thickest part. The measurements 
of length are given from point to point, and not around the curve. 
(ii.) There also occur oxea irregularly scattered throughout the sponge, 
and mixed with the above, which are rather longer and slightly more slender 
than the somal oxea. They are also quite straight, and taper gradually from 
the central point towards each end. When full-grown, they reach 14 mm. 
in length and 0-03 mm. in diameter. 
B. Microscleres. (Text-fig. 3, B.) 
The only microsclere is a euoxyaster, with pointed rays and very small 
‘centrum in most cases ; but a very few asters were seen in which a well- 
defined centrum was discernible. These asters form a dermal layer, and 
also occur scattered in very large numbers throughout the sponge. They 
measure from 6 w to 10 u in diameter. 
Locality. The single specimen in the collection was obtained at Tella Tella 
Kebira. 
Dnisiribution. Red Sea. 
Genus D1asTRA, n. gen. 
Hpipolaside with spherasters of two kinds, one a minute dermal spheraster 
and the other large and simulating a sterraster. 
The main skeleton consists almost entirely of a cortical layer of tangentially 
placed oxea. 
