MOORE—AUSTRALIAN MESOZOIC GEOLOGY. 241 
are continuously canaliculated; butit has not any thing approaching 
the angulated symmetrical arrangement of its skeleton fibres ; on the 
contrary, it very closely simulates the mode of disposition of the 
fibres that prevails in Dactylocalyx. The central canals in the fibres, 
in the species of Purisiphonia on which the genus is founded, occupy 
from about one-fifth to one-third of the entire diameter of the fibre ; 
they are straight and uniform in their diameter, and have little or 
no enlargements at their junctions with each other. The reticula- 
tions of the skeleton are frequently extremely close, so that the areas 
do not exceed, or sometimes even eaeal, the diameters of the fibres 
bounding nein, 
1. PurisipHonia Crarxet, Bowerbank. Pl. XVII. fig. 1. 
Sponge. Fistulose, branching, surface even. Oscula simple, dis- 
persed over the inner parietes of the fistule. Dermis and dermal 
membrane obsolete. Skeleton stout, closely reticulated. Interstitial 
cavities furnished with angulated sexradiate spicula? 
Loc. Wollumbilla, Queensland, Australia. 
Obs. There is much greater difficulty in the specific description of 
a fossil Sponge than of a recent one, as a considerable portion of the 
most decisive specific characters are usually absent, in consequence 
of the decomposition of the softer parts of the organization previously 
to fossilization ; and this is doubtless the case with the specimen 
under consideration. Although thus deprived of the use of many 
valuable descriptive characters, there are sufficient remaining to en- 
able us to securely determine its specific identity. 
It is difficult to say what was the real form of the specimen in 
its unmutilated state; but, judging by its present condition, it 
was originally a large fistular Sponge, giving off fistular branches 
at irregular intervals. The large fistular body of the Sponge has 
been split longitudinally, and a portion 4 inches in length, and 
almost half of the tube of the Sponge, remains; and from the sur- 
face of this the entire basal portions of two secondary fistular 
branches proceed; and there are also the remains of another such 
branch at the margin of the primary fistula at the right-hand side. 
The outer surface of the Sponge has an irregular reticulation of stout 
siliceous fibres, very similar to those of Dactylocalyw, immediately 
beneath the dermis. 
In all the recent species of this tribe of siliceo-fibrous Sponges 
with which I am acquainted, there is a free dermal coat attached to 
the stiff, non-expansive skeleton beneath, by connecting spicula, co- 
mented at their basal points to the mass of the skeleton by keratode 
only, and which would naturally be separated from the body of 
the Sponge, by maceration and decomposition of the keratode, a short 
period after its death ; and none of this dermal coat, it is probable, 
would appear with the fossil, unless if were to be enveloped and fixed 
in the matrix in a very short time after its death. This organized 
envelope usually affords the most distinct and determinative specific 
characters, and it was very important to discover its remains if pos- 
sible; but in this attempt I have been quite unsuccessful. In its 
