72 THE VICTORIAN NATURALIST. 



described in some detail because they show the development of 

 the canal-system from the simple type of L. stolonifer to the more 

 complex one of V. macera, and they show it in an unmistakable 

 manner. 



Reference has been made, again and again, to the presence of 

 spicules. They lie in the mesodermal tissue of the sponge, each 

 being developed from a single cell, the scleroblast, and are com- 

 posed of carbonate of lime, and give strength, support and 

 protection to the softer tissues. Three main forms can be dis- 

 tinguished : — The triradiates, which consist of three rays or arms 

 radiating from a common centre ; the quadriradiates with four 

 rays, the fourth ray projecting from the centre of the spicule in a 

 plane at right angles to that of the other three ; and the oxeotes 

 which consist of a simple rod usually spindle-shaped and pointed 

 at both ends. Specimens of the various kinds of spicules can be 

 obtained either by teasing up a piece of sponge with needles or 

 by boiling sponge tissue with a little potash. 



A few lines may be given here in reference to some interesting 

 fossil forms of members of this group occurring at Flinders. 

 About a mile westward of West Head, near the bathing 

 boxes, a small cliff-section of limestone rock of Eocene age is 

 within easy reach, where, mixed with fragments of polyzoa, 

 echinoid tests and brachiopoda, several varieties of sponges 

 occur. Examples of these were lately forwarded by Mr. T. S. 

 Hall, M.A., one of the vice-presidents of this Club, to Dr. G. J. 

 Hinde, F.R.S., who in the Quart. Joitrn. Geo!, Soc, vol. Ivi., 

 describes them as belonging to three new species. Two of them 

 require new genera for their reception, namely, Plectroninia and 

 Tretocalia, whilst a third form is referred to a genus, Bactronella, 

 which occurs in rocks of Jurassic age in Europe. The state of 

 preservation of this latter form enables Dr. Hinde to add to our 

 knowledge of the genus. Plectroninia is interesting in that it 

 belongs to the group of calcareous sponges with fused spicules 

 which so far is known to contain only this genus and a recent 

 Japanese form, the two together forming the group Lithonina. 

 Tretocalia and, possibly, Bactronella seem to be Pharetrones, but 

 better preserved specimens from clay beds are wanted to settle 

 the point. The Pharetrones were supposed to have become 

 extinct at the close of the Mesozoic period, but here we have 

 some Tertiary ones, while Professor Dendy regards one of our 

 recent Australian genera, Lelapia, as a living representative of the 

 same group. 



Further details as regards the anatomy of many of the local 

 forms of calcareous sponges can be obtained from the articles by 

 Professor Dendy published in the Proceedings and Transactions 

 of the Royal Society of Victoria and the Quarterly Journal of 

 Microscopical Science. 



