T. Davidson — Upper Silurian Brachiop)oda. 155 



principally in siliceous specimens or by sections, and not developed 

 in spar by the process Mr. Glass has discovered." I have recently 

 received a note from Mr. Whitfield, in which he informs me that in 

 the above statements I have been labouring under a mistake, that the 

 siliceous specimens he has worked out are comparatively few, and 

 that he has principally oper-ated on specimens filled with calc-spar — 

 these operations extending back for some years, and relating not only 

 to American, but also to a number of European forms, including some 

 from Bohemia and England. He says, " In fact I have treated my 

 specimens exactly as Mr. Glass has treated his." Mr. Whitfield 

 thus describes his method of operating — " I have been in the habit 

 of cutting down to near the spires with tools, then treating with 

 hydrochloric acid to render them more translucent, frequently 

 cutting longitudinally a little outside of the middle so as to get the 

 loop in profile. Athyris vittata, A. spiriferoides, Meristina nitida, and 

 M. Maria are all cut thus." Mr. Whitfield also refers to a friend of 

 his as having operated in a similar manner upon American specimens 

 of Atrypa reticularis, and upon European specimens of Tereb. 

 scalprum. Mr. John Young, of the Hunterian Museum, Glasgow, 

 has also, in the course of correspondence, informed Mr. Glass that 

 more than twelve years ago he operated upon four specimens — three 

 of Athyris ambigua, and one of A. Boysii — developing the spirals 

 from their sparry matrix by means of acid and a file and knife. 

 More recently, as I stated in my Carboniferous Supplement, Mr. 

 James Neilson, Jun., has developed in the same manner the spirals 

 in A. Boysii and Sp. lineata. 



As to the English forms worked out by Mr. Whitfield, I may 

 state that I have never seen any drawings of them — my knowledge 

 of the spirals and their connections in those of our English 

 Brachiopods which are filled with spar having been entirely derived 

 from the preparations of Mr. Glass. Mr. Glass, as he informs me, 

 does not lay any claim to the discovery that the Paleozoic spiral- 

 bearing forms of the Brachiopoda which are filled with spar are 

 favourable to the development of the spirals and their connections, 

 nor does he lay any claim to the first employment for such a 

 purpose of the knife supplemented by acid — though he was the first 

 to publish any account of such a process, and it was only after he 

 had done this that he became aware of its previous use. He thinks, 

 however, that his own method is somewhat different to that previously 

 employed. In the comparatively simple matter of developing the 

 spirals Mr. Glass has found through operating upon many hundreds 

 of specimens that to obtain the best and most finished results the acid 

 should first be used in removing the outer valve or valves when 

 they have not been transformed into spar. That then scraping with 

 a knife and frequent washing with water must be solely relied upon 

 until the spirals are clearly revealed without even a trace of the sparry 

 matrix upon them. Then to obtain a perfectly smooth surface, fine 

 emery cloth must be used, and finally the specimen must be dipped 

 for two or three seconds in the acid to remove the dullness of the 

 surface and to give to it a glossy and transparent appearance as if it 



