Dr. G. J. Hinde 07i the Genus Hinclia. 73 



the interspaces between the spicular mesh work would have 

 been occupied by the soft living structures of the sponge. 

 How could the borings therefore have been preserved if they 

 were made in the fleshy portion of the sponge, or in the canals, 

 when there are no traces of the soft structures themselves now 

 remaining, and both the spaces formerly occupied by these struc- 

 tures and the canals have since been infilled with solid silica? 

 Only on the supposition that the Palceachlya formed its own 

 tubes of sufficiently hard materials to resist all the subsequent 

 changes of fossilization can these dark threads in the siUceous 

 matrix of Hinclia be ascribed to this unicellular vegetable 

 parasite, and Prof. Duncan * does not attribute to it this 

 capacity. 



From the above considerations it seems to me evident that 

 whatever may be the nature of these tubes and dark filaments 

 in the siliceous matrix of the New Brunswick specimens of 

 Hinclia, they do not correspond to the characters of the boring 

 parasite, Palceachlya perforans, Dune, and therefore they 

 have no bearing whatever on the question of the original 

 mineral nature of the sponge. Some of these supposed 

 borings appear to me to be in reality the infilled axial canals 

 of siliceous acerate or acuate spicules, which have found their 

 way into the canals of the sponge. The faint outlines of the 

 walls of these spicules can in some cases be clearly distin- 

 guished ; but whether they are proper to the sponge or have 

 merely found their way into its canals from the exterior I am 

 not prepared to determine. I have noticed similar spicules 

 cemented to the outer surface of Tennessee examples of 

 Hinclia^ and I have also obtained them isolated by placing 

 specimens in acid. Spicules of this cliaracter not unfrequently 

 in the course of fossilization get their axial canals infilled 

 with dark solid materials, which remain as rods or threads 

 even after the spicular walls have been dissolved ; and I 

 believe some of the structures in the matrix of Hindia are of 

 this nature. The dark granules, which are either scattered 

 in the matrix or variously grouped to form the rods or threads, 

 are regarded by Prof. Duncan as the carbonized oospores of 

 the Palceachlya ; but by employing high powers many of these 

 granules can be seen to possess angular faces, and it has been 

 suggested to me by Dr. RaufF that they are in reality small 

 crystals of iron pyrites. 



* Prof. Duncan lias stated, however, in Quart. Journ. Geol. Soc. 1876, 

 vol. xxsii. p. 206, tliat he has observed the fossilized cellulose wall of 

 this very species of Palceuchli/a in the hard parts of a fossil Thamnastrma ; 

 but it would be far more wonderful to find its tubes and their contents 

 preserved after they had penetrated the soft parts and the empty canals of 

 this Silurian sponge. 



