10 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
only 10 mm. in maximum diameter and has but a simple vent. The colour in spirit is 
dirty white; the texture firm and compact, albeit somewhat cavernous at times. 
The canal system is leuconoid and quite typical. There is a rather thin and 
ill-defined ectosome, pierced above by the thickly scattered dermal pores and partially 
penetrated from below by the large, irregular sub-dermal cavities, if one may so term 
them. From the dermal pores short canals lead through the outer part of the ectosome 
into the sub-dermal cavities, many opening into each. The subdermal cavities 
pass down into the choanosome as large inhalant lacunee, breaking up into smaller 
lacunse as they go. The flagellate chambers are very thickly scattered through the 
ehoansome ; they are oval or nearly spherical, and measure about 0 086 mm. in diameter. 
The exhalant lacunae are similar to the inhalant, the principal ones leading into large 
oscular tubes which terminate at the vents. The oscular tubes are lined by a thin and 
rather ill-defined gastral cortex. 
The main skeleton of the sponge, that of the choanosome or chamber layer, 
■consists of thickly scattered triradiates arranged without any order. There is a well- 
defined dermal skeleton consisting of the following parts :—(1) In the outermost part 
of the ectosome a thin layer of triradiates arranged tangentially. (2) Again in the 
outermost part of the ectosome, a layer of microxea, arranged radially with slightly 
projecting outer ends. (These spicules appear to be almost, if not quite, absent in 
some specimens, though very numerous in the type). (3) Numerous, relatively large, 
more or less club-shaped oxea, arranged radially with the thick ends projecting from 
The surface and the thin ends penetrating through the ectosome and for a short distance 
into the choanosome. (4) Occasional bundles of very slender, hair-like trichoxea, 
arranged radially in the ectosome. (The extent to which these spicules are developed 
varies greatly in different specimens; in R.N. V, 1, they form fringes round the margins 
of the very minute vents, but this appears to be quite exceptional). The skeleton of 
the gastral cortex consists of a fairly thick layer of sagittal triradiates, with the paired 
rays turned towards the vent and much more strongly developed than the basal ray. 
Occasionally these spicules possess a short apical ray, the number of quadriradiates 
thus formed varying greatly in different specimens; they are very rare in the type, but 
numerous in R.N. V. 1. 
JSpicules :—- 
(1) Triradiates (fig. 8a); perhaps always more or less sagittal, with the oral angle 
wider than the paired angles, but ranging from forms in which the difference 
between the angles is but slight and the rays are of approximately equal length, 
to very strongly sagittal forms with the oral rays extended almost in a straight 
line and much longer and stouter than the basal ray (characteristic of the 
gastral cortex). The rays are fairly gradually and sharply pointed, and it is 
usual for the oral rays to be slightly curved or crooked while the basal ray is 
almost or quite straight. In a full-grown spicule with approximately equal 
rays the latter measure about 0 197 by 0 0184 mm. 
(2) Quadriradiates; formed by the addition of a short apical ray to triradiates of 
the gastral cortex. 
