254 



W. J. SOLLAS ON A NEW LYSSAKINE HEXACTINELLID 



18. On Astroconia Granti, a new Lyssaeine Rexactinellid from 

 the Silurian Formation" of Canada. By W. J. SoiLAs,Esq.,M.A., 

 F.R.S.E., F.G.S., Professor of Geology in University College, 

 Bristol. (Eead February 23, 1881.) 



By the great kindness of Lieut.-Col. Charles Coote Grant, I have re- 

 ceived a valuable collection of fossil specimens from the Silurian strata 

 of Hamilton, Ontario. I hope, as opportunity serves, to offer de- 

 scriptions of the more interesting of these fossils, and in the following 

 short paper make a beginning by describing an incompletely silici- 

 fied specimen of chert, which by its remarkable similarity to the chalk- 

 flints of Trimmingham arrested my attention when studying those 

 bodies. The specimen in question is a small piece (1 inch cube) of 

 greyish siliceous dolomite with a gritty granular texture ; on one 

 face it bears a carbonized Hydrozoon, on another a silicified Polyzoon, 

 and on a third shows the opening of a long winding cavity which 

 extends into the interior. From the sides of this cavity some long 

 cylindrical rods, very suggestive of sponge-spicules, were seen 

 conspicuously projecting : under the microscope by reflected light 

 they were seen to be covered with an irregular crystalline deposit, 

 which made the resemblance to spicules less striking than when exa- 

 mined by the unassisted eye. The specimen was now broken into two 

 pieces, and the part containing the rods and cavity placed in dilute 

 hydrochloric acid. Solution with faint effervescence took place ; and 

 after standing for twenty-four hours the supernatant liquor was 

 poured off for subsquent examination, while the sediment and 

 small piece of siliceous dolomite remaining were well washed and 

 further examined. From the sides of the cavity in the dolomitic 

 chert, cylindrical rods were still seen projecting, and under the 

 microscope were found to have lost their irregular outline and 

 at the same time to have somewhat diminished in thickness ; 

 evidently a crystalline coating had been dissolved away from them ; 

 and in the slender siliceous rods which remained one recognized at 

 once true sponge-spicules. 



The sediment was next examined. It contained a number of large 

 siliceous spicules, some of which are figured on page 255, also some 

 small colourless transparen t hexagonal prisms capped with six-sided 

 pyramids at each end, evidently quartz crystals, and, finally, some 

 minute rhombohedra, which were subsequently found to be mag- 

 nesite. 



The Sjjonge-Sjncules. — By reflected light the spicules appear snow- 

 white, with a vitreous lustre ; by transmitted light they are glassy and 

 translucent ; when immersed in water, glycerine-jelly, or Canada- 

 balsam, they become quite transparent, except in places where they 

 are traversed by a minute black spongy network which appears 

 white and shining with reflected light, and. evidently contains air : 

 when this is displaced by the liquid medium, the spicule becomes 



