176 
THE VOYAGE OF H.M.S. CHALLENGEE. 
deeper in tint, almost orange coloured ; the lower surface where not exposed to the light 
of a pale grey tint. 
Habitat . — Station 162, off East Moncoeur Island, Bass Strait, April 2, 1874 ; lat. 39° 
10' 30" S., long. 146° 37' 0"E. ; depth, 38 fathoms; bottom, sand and shells. Dredged. 
Remarks. — Of this conulose Stellettid a single specimen was dredged ; it measures 
from 45 to 50 mm, in diameter. The conules vary from 1 to 5 mm. in height. There 
are three evident oscules situated near the base of the sponge, and indications of others ; 
of the three, the two smaller are about 2 mm. in diameter, the third larger is about 5 
mm. in diameter. The two smaller oscules open each at the base of a conule which over- 
hangs them, the third larger is situated on the summit of an irregular tent-like elevation, 
with a conule at each side of its margin. It leads inio a system of wide intercortical 
canals (constricted into vesicles by numerous vela), which receive the excurrent canals 
from the choanosome through sphinctrate apertures. 
The pores of the pore-sieves are very small, usually from O' 008 to 0'015 ram. in 
diameter, they lead into widely extending intercortical cavities, which are converted by 
numerous velar partitions into a network of vesicles, and which communicate with the 
incurrent canals of the choanosome by descending radial canals. 
The cortex (PI. XXXVIII. fig. 2), about 2 or 3 mm. in thickness, consists almost 
entirely of fibrous tissue, the fusiform cells of which run in various directions concentric 
with the surface. Embedded in the tissue are abundant angular grains of quartz sand, and 
occasional Foraminifera and other foreign bodies, usually ranging between 0’08 and 0'5 
mm. in diameter, on the average about 0'2 mm. The presence of these sand grains makes 
it impossible to obtain other than very thick slices of the cortex. The mesoderm of the 
choanosome is a sarcenchyma, except where it forms the walls of the larger canals ; these 
are collenchymatous. 
Skeleton . — The megascleres are arranged in radial bundles, and the trisenes and 
cladoxeas are first met with in the choanosome just below the cortex. The remarkable 
cladoxeas are more numerous than the trisenes, occurring as the staple cladose spicule of 
the skeleton. This is the case in no other known Tetractinellid, for though similar forms 
may occasionally be found where the spicules are unusually massive and densely packed, 
as in Ecionema 'pyriformis, they are never other than exceptional and evidently 
abnormal varieties. These abnormal varieties are, however, of the highest interest, 
since the conditions which have exceptionally operated to produce them in one sponge 
may become general in their action in another, and thus lead to the multiplication of 
the abnormal into the characteristic or prevailing form. Of this process the instances 
afforded by the sponges are almost numberless, one of the commonest being the abnormal 
occurrence of oxystrongyles, strongyloxeas, and strongyles in skeletons composed other- 
wise solely of oxeas. It is in the study of these changes that we may find a clue to the 
