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1910. | Pharetromd Sponge from Christmas Island. 129 
in layer upon layer of flakes, and here and there sutural lines can be seen 
between masses of flakes. Even under a low power, the microscopic 
structure is seen to be coarsely fibrillar (Plate 11, fig. 16), the fibrille 
radiating usually in a fan-like manner. Sometimes the flakes are circular 
or long oval in shape, with the fibrille radiating out all round, and more or 
less in one plane. The fibrille under a high power show conical projecting 
ends, and are separate and distinct for a little distance below the surface 
(Plate 11, figs. 14, 15). 
In two places in the ground-down sections of a whole specimen, an axial 
spicule appeared to be present in the strands, but under higher powers 
the appearance was seen to be due to interior flakes of elongated shape 
with the fibrille arranged on each side of a smooth central raphe. If I 
had found merely some relic of a spicule—but I failed to do so after 
a most careful search—I would still have regarded the skeleton as a new 
type of construction. 
The spicules are all triradiate, but of different shapes, viz. :— 
(a) Equiangular, equal-rayed or nearly equal-rayed, pyramidal, that is, 
with the ends resting on a plane different from the meeting-point of the 
rays. The rays are 55 long, and 10 thick at the base, with blunt or 
rounded ends. These spicules are mostly found in the poral area, where 
they form a polygonal network (Plate 11, figs. 17, 18), but they also occur in 
the layer beneath the dermal scales. 
(6) Nearly sagittal, and irregular triradiates with unequal rays and 
angles (Plate 11, figs. 19, 23, 24). Plate 11, fig. 19, shows a spicule with 
rays 130, 98, and 65,4 in length, by 10 thick. Plate 11, fig. 23, shows 
a form transitional between an ordinary triradiate and a tuning-fork. 
(c) Tuning-fork spicules, found isolated or united into little “fibres” of 
two or three below the dermal scales. These spicules vary greatly in form, 
some being very bizarre (Piate 11, figs. 20-22, 25, 26). Fig. 20 has the short 
prongs curved and bent inwards, the total length is 87 uw, the prongs being 
18 w long and 10 w thick at the base; in another example one prong is only 
16 w long, and the other 65 p. Spicules a, b,c, form a thin scattered layer 
between the dermal scales and main skeletal framework. 
Plate 10, fig. 6, shows the under surface of a scale with a few “ fibres” or 
bundles each composed of two or three tuning-forks adhering to it. 
The remarkable dermal scales or plates are imbricated so that the free 
edges are directed either towards the oscule or the poral groove (Plate 10, 
fic. 3B). Some, however, are wholly uncovered by others. The scales are 
mostly nearly circular in outline, though some are oval and a few triangular 
with rounded angles (Plate 10, fig. 6, and Plate 11, figs. 10, 11). 
