Group I. (fine 



150 



of one and the same piece of rock. When united the two 

 pieces measure one and a quarter inches long, one and a half 

 inches wide, and three-quarters of an inch thick, the spicular 

 rods extending throughout. 



I am indebted to Mr. Howchin for the following remarks 

 [August 31, 1916]: — 



"From the material in my hand I think there must be at 

 least two clearly distinct species. Notwithstanding the 

 inclusion of rods of different diameters in the same individual, 

 there is, in all my examples, a certain preponderance of a 

 given diameter in the rods of any one particular sponge. 

 This also seems to be borne out by the descriptions and figures 

 hitherto published. That is to say, in a certain number of 

 cases the individual rods do not, throughout the entire speci- 

 men, attain a diameter of more than half that of the average 

 size of other examples. The diameters of the respective 

 species, as described, are as follows (Hinde's figures being 

 used) : — 



r Hyalostelia parallel a, McCoy, 0*2 to 



0'5 mm. 

 H. (Pyritonema) fasciculus, McCoy, 0*2 

 hair-like rods). ) to 0'5 mm. 



\ R . (Hyalonema) youngi, Eth., junr. 

 ( Described as "hair-like." 



(Hyalostelia australis, Eth., junr., 0'19 to 



Group II. J 1*39 mm. 



(stout rods). "J 77. (Hyalonema) smithii, Y. and Y., 0'3 



( to 1'5 mm. 



"It is true that H. australis (rods) do 'considerably 



exceed' in size those of Pyritonema fasciculus, but they are, if 



anything, a little smaller than those of 77". smithii. The 



Tempe Downs example comes so near to the Carboniferous 



77. smithii that I regarded it as indistinguishable from that 



form, and for that reason did not define it as a new species." 



EXPLANATION OF PLATE XVI IT. 



Hyalostelia australis, Eth., fits. 



Fig. ]. Transverse section of anchoring spicules x 4 diam. 

 ,, 2. Longitudinal section of several spicules — x7 diam. 



In both sections the dense black portions in the .spicules are 

 the silicified tissue; the white patches, on the contrary, are the 

 blebs of chaleedonic silica. In the transverse section (fig. 1) 

 some of the axial canals are visible (as at a J. and again in a 

 longitudinal section (fig. 2, b). 



