FEOM THE LOWER CALCAREOUS GRIT OF YORKSHIRE. 61 



Fig. 4. A transverse section of a fragment of the wall-plates, enlarged twenty 

 diameters, showing its structure of globate spicules. In this specimen 

 the sponge is imbedded in a matrix of transparent granular calcite. 



5. Several of the globate spicules, obtained by dissolving in acid the rock- 



matrix in which one of the sponges is partially imbedded, showing 

 variations of form and size. Enlarged sixty diameters. 



6. A globate spicule, enlarged two hundred diameters, showing the minute 



points on its surface produced by the distal ends of its component 

 siliceous fibres. The specimen is mounted in glycerine. 



7. A portion of the surface of a globate spicule, showing the markings 



enlarged to six hundred and sixty diameters. 



8. A globate spicule, enlarged two hundred diameters, showing traces of its 



component radial fibres. The specimen is mounted in C;;nada balsam. 



9. A globate spicule, enlarged two hundred diameters, showing the effects 



of corrosion on its surfece, whilst the interior has been replaced by 

 banded chalcedony. Mounted in glycerine. 

 10. A similar spicule, showing central replacement, whilst the surface 

 remains unaltered. Mounted in Canada balsam. 



Discussion. 



The President said that palaeontologists were greatly indebted to 

 Dr. Hinde for his researches on sponge-structure. They would espe- 

 cially welcome these details on an entirely new form. He noticed 

 the apparent anomaly of " globates " being called " spicules." 



Mr. HuDLESTON had been greatly interested in the results of this 

 particular piece of work, since it helped to clear up some disputed 

 points in connexion with the Corallian rocks of Yorkshire. These 

 microscopic globates, though swarming in parts of the Lower Cal- 

 careous Grit, were far from uncommon in portions of the Coral Eag. 

 He had been struck with the amount of chalcedonic silica in certain 

 portions of the Rag, and had ejideavoured to ascertain its source. 

 The rock-sections prepared for this purpose W'cre full of small 

 granular bodies, which Prof. Sollas pronounced to be globates of a 

 siliceous sponge such as Geodia. The difficulty, of course, was to 

 account for the absence of the elongate spicules, and Mr. Hudleston 

 admitted that his own remarks on this point at a time when no one 

 had any suspicion of a sponge whose spicules were all globates, 

 might be open to correction. But since elongate spicules are 

 traversed by a canal, where the action of solvents first shows itself, 

 he still thought it possible that they might disappear as soon, if 

 not sooner, than the more microscopic globates. The Author 

 thought otherwise. Anyhow, the problem, which had puzzled 

 Mr. Sorby and led to so much discussion, was now conclusively solved 

 by the recognition of the true nature of the Scai'borough fossil, — 

 one of the many results of Dr. Hinde's intimate acquaintance with 

 sponge-structure. 



The Author, in reply, said that he agreed wilh tlie remarks of 

 the President as to the anomaly of the term " globate " spicules, but 

 the word "spicule " might be advantageously employed in ageneuil 

 sense for the. small bodies which compose the skeletons of sj)onges. 

 He did not think that Mr. Hudleston was much to blame for referring 

 the detached globates to Geodia, as he himself had been quite asto- 

 nished at the discovery of such a sponge as the one now described. 



