IV PREFATORY NOTE TO VOL. II. 



by observers so competent and laborious as Drs. Greville, Arnott, 

 Gregory and others, and the liberality with which their disco- 

 veries and opinions are communicated to the public and myself, 

 justify the expectation which I entertain of being able shortly 

 to increase the utility of my work by a valuable accession of 

 new facts and new forms. 



I think it right in this connexion to state, that I have no 

 additional evidence enabling me to receive the genus Didyoclia 

 as belonging to the Diatomacese, and that various features in 

 the structure of the species arranged under the genera Clueto- 

 ceros, Goniothecium, and their allies, constrain me for the present 

 to refuse such forms admission into the present work. An ad- 

 mirable paper by Mr. Brightwell on the British and Foreign 

 Species of some of these genera may be found in the ' Microsco- 

 pical Journal' for January 1856, and will, it is to be hoped, 

 direct the attention of Naturalists to the determination of the 

 true character and position of these singular organisms. 



Queen's College, Cork, March 1856. 



