340 THE AMERICAN MONTHLY [Dec 



sues. Three main forms cau be distinguished : — The 

 triindiates, which cousist of three rays or arras radia- 

 ting 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 usu- 

 ally spindle-shaped aud pointed at both ends. vSpecimens 

 of the various kinds of spicules can be obtained either by 

 tearing 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 in- 

 teresting 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. Gr. J. Hinde, F.R. 

 S., who in the Quart. Jouru. Geol. Coc, vol. Ivi., describes 

 them as belonging to three new species. Two of them re- 

 quire new genera for their reception, namely, Plectroni- 

 nia 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 aud, possibly, Bactronella seem to be Phare- 

 trones, but better preserved specimens from clay bedff are 

 wanted to settle the point. Pharetrones were supposed 

 to have become extinct at the close of the Mesozoic peri- 

 od, but here we have some Tertiary ones, while Profes- 

 sor Deudy regards one of our recent Australian genera, 



