346 MARINE BIOLOGY OF THE SUDANESE RED SBA. 
Skeleton arrangement. 
The main skeleton, which is also the dermal skeleton, owing to the peculiar 
character of the sponge, consists of an irregular reticulation of spicular fibres, 
which run tangentially just under the surface of the sponge. The spicules 
composing them are tylota, and there are usually several (six or eight) rows 
of spicules in the fibres. These fibres run quite irregularly, but do not seem 
to branch or anastomose. 
In addition to these spicular fibres, there occur very large 
numbers of spined styli, which are arranged vertically to the 
surface. They occur scattered singly over the sponge surface 
and are fairly evenly and regularly distributed over the whole 
sponge. Asarule, they project for about half their length 
from the sponge surface. 
Spicules. (Text-fig. 21.) 
A. Megascleres. 
(i.) Tylota. 
The tylota are straight, slender spicules, with very slight 
heads. As was noticed in Mywilla cratera, the distal ends of 
the head are pointed instead of being rounded, and in the 
present species it is even more noticeable than in the former. 
They are, as a rule, about 0°16 mm. long, and the shaft, which 
is of almost the same thickness for the whole of its length, 
measures 0002 mm. in diameter. The head does not exceed 
0:003 mm. in diameter in most of the specimens, but a few 
were seen with large swollen heads, very similar to those of 
Suberites. These spicules are probably foreign. 
(ii.) Styles. 
The styli are all thickly covered with fairly long spines, 
Fig, 21.—Myailla 
tenwissima. ; ; 
Spicules, x 650. towards the head. They vary very considerably in length, 
probably owing to the variation in thickness of the sponge- 
and throughout their whole length; also the spines are largest 
film, and all measurements of length may be found between 0°05 mm. and ° 
0115 mm. The diameter of the head of the spicule, excluding the spines, 
measures 0-004 mm. 
B. Microscleres. 
The only microscleres present in this species are tridentate isochelee, which 
occur sparsely scattered throughout the sponge. The shaft of the chela is 
curved, almost bow-shaped, and the head is well developed. The chela 
measures 0°02 mm. to 0°024 mm. in length. 
Locality. All three specimens were obtained in Suakin Harbour, in 
5 fathoms of water. 
Distribution. Red Sea. 
