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Monday, 19f^ December 1853, 

 Sir T. M. BKISBANE, Bart., President, in the Chair. 



The following Communications were read : — 



1. Additional observations on the Diatomaceous Earth of 

 Mull, with a notice of several new species occurring in 

 it, and Remarks on the value of Genei'ic and Specific 

 Characters in the Classification of the Diatomacese. By 

 William Gregory, M.D., Professor of Chemistry. 



The author, after mentioning his previous communications on this 

 subject, stated, that continued investigations of the deposit had 

 yielded the extraordinary number of about 150 species of Diatoma- 

 ceae, and that as several of these had been only recently observed, it 

 was nearly certain that more yet remained. 



Of these species, from 12 to 15 appear to be undescribed, and 

 there are also 7 or 8 new to Britain, or not hitherto admitted as 

 British species. 



The following hst contains the names of 118 known and described 

 species occurring in the Mull deposit : — 



List of admitted British Species of Diatomacees found in the Mull 

 Deposit up to SOth November 1853. 



