PREFACE. in 



followed in these plates, but this was impracticable, as the earlier figures had to be 

 engraved before the entire collection was examined. 



To the late lamented Professor Sir Wyville Thomson 1 lie under a permanent debt of 

 gratitude for the opportunity afforded me of examining and reporting on this interesting 

 group of organisms, and my best thanks are also due and rendered to Mr John Murray 

 for the valuable aid of all kinds which he has given me in my work ; as well as to Mr. 

 John Rattray of the Challenger Editorial Staff for the care and pains he has taken with 

 the proof sheets as they were passing through the press, and for many valuable suggestions. 

 To Dr Radford, Mr J. A. Tulk, Dr Stolterfoth, and Mr Weissflog of Dresden, who 

 have manifested the greatest interest in my work, and have often furnished me with 

 valuable advice, I also lie under the deepest obligation, and last, but not least, to Dr 

 James Rae, R.N., who has with the greatest liberality furnished me with many unique 

 preparations of new and rare frustules. 



Although no one can be more conscious of the many imperfections of the work than 

 the author himself, it is earnestly hoped that these are not of a kind to derogate too 

 much from its value as a work of reference on this exceedingly interesting branch of 

 marine investigation. 



