370 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
The present genus is an unsatisfactory one, but the specimens for which it 
has been created would not go into any of the previously named genera 
without considerably widening the generic diagnosis. Its nearest ally is 
undoubtedly Heteronema, but it differs from the latter genus principally in its 
much less regular skeleton, which has apparently undergone partial de- 
generation in Duriella, Here a very wide-meshed network 1s marked out by 
what I propose to call “ fibre-lines”” composea not of one fibre, but of a very 
irregular reticulation of small fibres. At the junctions of the various fibre- 
lines a considerable increase in the thickness of the fibres occurs, and also an 
increase in the number of fibres, which widen out into a system of diagonal 
connecting-fibres between the main “ fibre-lines.” 
DURIELLA NIGRA, n. sp. (PI. 41. fig. 29.) 
The single specimen consists of two irregular upright somewhat cylindrical 
processes varying in different parts from 20 mm. to 30 mm. in diameter and 
135 mm. high. 
The surface is minutely conulose, very like that of Heteronema erecta, with 
conuli 0°5 mm. to 1:0 mm. high, and 1:0 mm. to 1°5 mm. apart. As in 
Heteronema, these conuli are connected with one another by a series of ridges 
radiating from each one, so that the surface presents a minutely reticulate 
appearance. 
The oscula are numerous, and occur scattered about the surface of the 
sponge promiscuously and irregularly. They measure 3 mm. to 4mm. in 
diameter. : 
The pores occur thickly scattered over the surface of the sponge, in the 
meshes between the ridges connecting the conuli. 
The skeleton consists of an irregular, very wide reticulation of “ fibre-lines,” 
the mesh averaging 2 mm. to 3 mm. across. ‘The fibres composing the 
“ fibre-lines” are arranged very irregularly in the “line ” and vary enormously 
in size, fibres of all diameters from 0°03 mm. to 0°3 mm. being found. As a 
rule, the thickest fibres are found near the junction of the radial and tangential 
“ fibre-lines.” 
At the surface of the sponge there is a tangential reticulation of fibres, 
which is arranged rather more regularly than those in the interior of the 
sponge. The external evidences of this reticulation can be seen in the ridges 
radiating from the conuli. The conuli themselves are the meeting-points of 
a large number of fibres, each of which underlies a ridge. Between these 
fibres there run very numerous smaller fibres which do not show on the 
surface. The general average of size of the fibres is higher in the dermal 
reticulation than in the skeleton of the sponge interior, but the individual 
fibres of the former do not exceed those of the Jatter in size. 
All the fibres are full of foreign bodies such as sand-grains, sponge-spicules, 
and Radiolaria skeletons. 
