Yol. 56.] FROM THE EOCENE OF VICTORIA.. 61 



they are not fused together. The spicular rays are from 0*025 

 to 0-05 mm. long, and about 0-01 mm. thick. In addition to the 

 irregular spicules, there are in the basal layer a few simple three- 

 and four-rayed spicules, having the facial rays approximately in 

 the same plane (PL V, figs 5-8). 



Neither simple rod-spicules nor tuning-fork spicules have 

 been observed in the basal layer or in any other part of the 

 sponge. 



The four-rayed spicules of the main skeleton have the facial rays , 

 disposed in tripodal form • they are short, of nearly equal thick- 

 ness throughout, with obtuse or expanded terminations ; they 

 are from 0*06 to 0-13 mm. in length, and about 0-025 mm. in 

 thickness (PI. Y, figs. 15, 17-19). They are connected together 

 by interclasping and by fusion as well. The apical rays gradually 

 taper to a delicate point ; they are, when complete, distinctly longer 

 than the facial rays. Near the outside of the sponge these apical rays 

 are free and project outward ; in the interior of the sponge-wall they 

 are connected transversely, by peculiar small four-rayed spicules, to 

 adjacent apical rays. These connecting spicules (PI. Y, figs. 9, 

 12, 13) have two of the facial rays in one line; they are usually 

 furnished with lateral prickles, and they terminate obtusely or 

 expanded. They appear to be often fused as well as intimately 

 fitted to the apical rays of the main skeletal spicules, and they give 

 the appearance of lattice-bars crossing the radial lines of the 

 skeleton (PI. Y, fig. 15). Similar connecting spicules are well 

 marked in Petrostroma Schukei. 1 



These sponges are scarcely, if at all, affected by fossilization, for 

 the spicules are as bright and glassy as those of recent forms, and 

 their finest details are preserved. The surfaces of the spicules of the 

 basal layer and of the younger skeletal forms are smooth and even, 

 while in the mature skeletal spicules the surface is covered with 

 minute tubercles similar to the investing pellicle of the mesh-fibres in 

 Plectroninia Halli. Some of the larger skeletal spicules are 

 penetrated thickly in all directions by the minute interlacing borings 

 of an alga (?) in much the same way as the skeletal tissues of 

 recent and fossil corals. 



Distributio n. — These small forms were discovered in a coll ection 

 of polyzoa from Mount Martha or Mornington, by Mr. B. W. Priest, 

 who recognized them as sponges and submitted them to me for 

 examination. Mr. T. S. Hall, of Melbourne, informs me that the 

 Mount Martha or Mornington beds are well known for their richness 

 in fossils ; they are situated about 30 miles from Melbourne. Only 

 a small outcrop, a few chains in length, is now to be seen. The 

 late Sir Frederick M'Coy called the beds Upper Eocene at first, and 

 afterwards Oligocene. Prof. Ralph Tate, of Adelaide, has furnished 

 detailed evidence of their Eocene age, and his view on this point 

 is now generally regarded as correct. 



1 Zool. Jahrb. vol. x (1898) p. 25 & pi. ii, figs. 19-25, pi. iii, figs. 20, 21, 23- 

 25, pi. iv, fig. E. 



