_DENDY—REPORT ON THE CALCAREOUS SPONGES 9 
equiangular and equiradiate spicules, which may become sagittal at the oscular margins. 
Radiates of the chamber layer with no definite arrangement, but irregularly scattered 
in the walls of the large elongated chambers, or between the small spherical chambers. 
No subgastral sagittal radiates. Nuclei of collared cells probably always basal. 
Genus Leucascus Dendy. 
Flagellated chambers greatly elongated, tubular, and sometimes copiously branched. 
Section A. 
No oxea present. 
3. Leucascus simplex Dendy [1892]. 
(Plate 1, fig. 5; Plate 4, fig. 1.) 
This species is represented in the collection by a considerable number of examples 
encrusting the branches of several specimens of a small gorgonid.. The sponge forms 
uregular, more or less lobulated, cushiony masses (Plate 1, fig. 5), with small vents 
occurring singly here and there in prominent positions. Examination with a pocket lens 
shows the thin, pore-bearing dermal membrane, the groups of inhalant pores being 
especially conspicuous over the ends of the radially disposed inhalant channels. The 
colour in spirit is light brownish yellow and the texture soft and compressible and 
rather fragile. 
The canal system agrees precisely with that which I described in the case of the 
Australian specimens, and of which I gave an illustration in my “Studies on the 
Comparative Anatomy of Sponges,’ Part V [1893, fig. 1]. The flagellated chambers 
are very long, copiously branched, and with their blind, outer ends directed more or 
less at right angles towards the dermal surface, where they are covered over by a thin 
cortex formed by the spiculiferous, pore-bearing dermal membrane. Internally the main 
stems of the branching systems of chambers open into wide exhalant canals which 
converge towards the vents. The thin walls of these exhalant canals are not lined 
by collared cells, but they are strengthened by numerous spicules. 
The blind ends of the branches of the radial chambers form a sort of reticulate 
pattern beneath the thin dermal cortex, in the meshes of which lie the outer ends of the 
large inhalant channels, which run in between the groups of chamber-branches at right 
angles to the surface. 
The skeleton consists of triradiate and quadriradiate spicules of fairly uniform size, 
irregularly scattered in the walls of the radial chambers and of the exhalant canals, and 
likewise in the dermal cortex, but nowhere forming more than a thin layer, though of 
course with overlapping rays. 
The spicules (Plate 4, fig. 1) are all regular, with moderately stout, gradually sharp- 
pointed rays, measuring about 0°1 mm. in length by 0:01 mm. in diameter at the base. 
In the walls of the exhalant canals many of them have well-developed but slender, 
straight or nearly straight, very sharp-pointed apical rays, projecting into the lumen 
SECOND SERIES—ZOOLOGY, VOL. XVI. 2 

