70 MARINE BIOLOGY OE THE SUDANESE RED SEA. 
There are no nutritive canals in the axis. A longitudinal section shows 
that the axis is built up of minute spindle-shaped spicules, fused together, 
and arranged with their long axes in the line of the long axis of the 
branch. 
The nodes are much shorter than the internodes (8-4 mm.) and are some- 
what thicker. They are composed of a dark-red horny substance, which, 
under the microscope, appears as a yellowish network with numerous red 
spindle-shaped spicules in the meshes. 
It occasionally happens that a branch arises from an internode ; in such 
cases the first joint is horny. 
The cream-coloured coenenchyma is crowded with small spicules. Most of 
these are white, but some are tinged with yellow or yellowish green. Spiny 
clubs and more warty double-clubs and dumb-bells are very abundant. 
Spindles bearing numerous very minute warts are less common, and simple 
spindles are rare. 
The following measurements were taken of length and breadth in milli- 
SUPE = 
Clubs : 0°136 x 0°084; 0°153 x 0:059; 0:119 x 0-051. 
Double clubs: 0°042 x 0:084: 0:067 x 0:055; 0:051 x 0-042. 
Spindles : 0:°187 x 0:051; 0:119 x 0-025. 
Red spindles of nodes: 0°102 x 0-017; 0:085 x 0:017; 0-068 x 0:002. 
The small polyps are spirally arranged almost uniformly all round the 
branches. They are nearly all retracted, lying almost flush with the surface 
of the coenenchyma. Besides the substantial anastomosis, there may be a 
more superficial fusion of coenenchyma when one branch lies against another. 
Locality.—Coral-reef, Mersa Makdah, Shubuk. 
CLATHRARIA AcuTA, Gray. (Plate 7. figs. 3 & 4.) ! 
See Gray: Catalogue of the Lithophytes in the British Museum, 1870, p. 12. 
This species is represented by two specimens, one of 7 em. and the other of 
5 em. in height. The mode of growth is tree-like and graceful. The 
branches, much more slender than in C. rubrinodis, are cylindrical and of 
very uniform width until close to their end, when they narrow abruptly into 
a sharp apex. 
In the larger specimen there is a main stem, which gives off two long 
branches on one side, two long and three short on the other, and then bifur- 
cates at the top. The side branches also show dichotomy. Of the seven 
branches four arise from the internodes. The other specimen is branched 
dichotomously throughout and the branches arise from the nodes. On the 
whole the branching is in one plane. There may be fusion of branches, but 
not nearly to the same extent as in C. rubrinodis. 
The colour of the preserved specimens is a delicate flesh-pink, marked by 
