360 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
MEGALOPASTAS ERECTUS, n. sp. 
The single specimen that was obtained of this new species is a small 
upright sponge, in the form of a rather wide and fairly thick mass. It 
is formed of a number of lobes, all more or less fused together and ot 
irregular shape and varying size, and measures 65 mm. wide, 40 mm. high, 
and from 8 mm. to 20 mm. thick from side to side. The specimen is 
thickest at the centre, and gradually thins out to the sides. 
The surface is covered with small conuli, from the summits of which the 
fibres of the skeleton project. They are very small and scattered irregularly 
over the whole surface. They do not exceed 1:0 mm. in height. 
The oscula are very few and irregularly scattered over the sponge. They 
measure about 3 mm. to 4 mm. in diameter. 
The pores were not distinguishable. 
The colour of the sponge in spirit is deep violet. 
The texture of the sponge is firm and gelatinous, yet easily broken. 
Skeletal arrangement. 
The skeleton is intermediate between that of a typical Dendrilla, in which 
there is a tree-like skeleton, and that of a typical Megalopastas, in which 
there is a reticulate skeleton. In the most typical members of the latter 
genus this skeletal reticulation is very regular, and primary and secondary 
fibres are clearly differentiated. 
In the species now under consideration there are no distinct primary and 
secondary fibres and the reticulation is quite irregular ; in fact, it is only 
after considerable hesitation that the species has been placed in Megalopastas 
rather than in Dendrilla. The skeleton consists of fairly large fibres, which 
branch very frequently and anastomose with each other here and there. No 
definite or average size can be given for the meshes of the reticulation thus 
formed, as the size varies enormously, and sometimes long stretches of 
skeleton-fibre occur without any anastomoses at all. 
The fibres are solid, and do not possess a core of foreign bodies; they vary 
considerably in size, but do not seem to exceed 0-11 mm. in diameter. 
Canal-system and Chambers. 
The whole sponge is traversed by very many wide canals, so that in section 
it appears almost cavernous. These canals run in a direction approximating 
to the radial, down into the sponge, though the actual direction of the canal 
must necessarily vary as it branches. | 
The chambers are wide and elongated, and occur in large numbers 
throughout the sponge. They measure 0:2 mm. long at the maximum, by 
0:04 mm. wide. They open by wide mouths direct into the large exhalant 
canals. 
