149 



casts are larger than Hyalostelia rods proper, Tate yielded 

 preference to a sponge view of their nature rather than 

 regard them as Annelide burrows. 



The cylindrical rods forming the specimen now before me, 

 and which I propose to term Hyalostelia australis, have a 

 variable diameter of 0'19-1"39 mm., the longest preserved 

 piece measuring twenty millimetres. They are circular in sec- 

 tion, and when the strong mineral alteration the rods have 

 undergone allows the structure to be seen, it is concentric. In 

 many an axial tube is still apparent. These spicular cables 

 are quite free and unattached to one another, without any 

 trace of "rope-like bundles," and although not all absolutely 

 parallel to one another, lie more or less in one direction. 



The matrix is a compact quartzite slightly iron-stained in 

 colour, and the rods being white stand out in strong contrast. 



As already stated, the spicular rods are siliceous like the 

 matrix, but in places have undergone a secondary chalcedonic 

 change, and when this is so all structure is obliterated, the 

 alteration taking the form of bleb-like particles. Neither 

 hooked-like terminations nor projecting decorative structures 

 were observed. 



The variation in the spicule diameter (0*19-1'39 mm.) 

 is quite in keeping with that of the already-described species, 

 //. fasciculus, McCoy, sp. ('15-'7 mm.). Dr. J. G. Hinde 

 comments on this variability in the anchoring spicules of the 

 above species, ( 4) which is met with in limestones of Llandeilo 

 age; these also are converted into chalcedonic silica. 



The diameter of the MacDonnell Ranges anchoring 

 spicules, therefore, very considerably exceeds that of the 

 British form, and will afford a ready means of distinguishing 

 the two until the body of the sponge proper in H . australis 

 is discovered. 



As a matter of strict priority the name Hyalostelia, 

 Zittel, 1878, should give place to that of Pyritonema, McCoy, 

 1850. Dr. Hinde, however, has retained the former, but in 

 the English edition of Zittel's "Text-book of Palaeontology, " 

 by Eastman/ 5 ) the two are separately maintained, Pyrito- 

 nema being denned as "fascicles of long, stout spicules, 

 supposed to be root tufts"; whilst in Hyalostelia the anchor- 

 ing spicules are "root-tufts composed of elongated, slightly- 

 bent fibres, sometimes terminating in four recurved rays." 



Mr. Howchin was kind enough to lend me his specimen, 

 when I found that it and the Museum example form portions 



(4) Hinde: Man, Brit. Foss. Sponges, pt. 2, 1888, p. 112. 



(5) Vol. i., 1900, p. 55. 



