PREFACE. 



The siliceous epiderms of the Diatomaceae have, of late years, 

 furnished the microscopist with a series of objects, not merely 

 attractive to the general observer, from the elegance of their forms, 

 but interesting to the more scientific student from the minute 

 complexity of their structure, whose detection and delineation call 

 into requisition the exercise of the most patient observation and 

 the skilful management of the highest powers of his instrument. 

 Much attention has in consequence been drawn to these minute 

 organisms, and the want of some English manual, containing a 

 classified arrangement and description of species, has been ex- 

 tensively felt. The present work has been undertaken to supply 

 this want, and owes its appearance to the enterprise and libe- 

 rality of the eminent opticians whose names appear on the title- 

 page. While securing me from loss, these gentlemen have placed 

 me under no inconvenient restrictions, and have left me at 

 liberty to render the work, as far as possible, a record of the 

 facts at present known with regard to the Diatomacese. So little, 

 however, has been published upon the subject by English natu- 

 ralists, and my views of structure and classification difler so 

 widely from those of continental writers, with whose works I am 

 acquainted, that I have found it necessary to make the following 

 pages little else than a record of individual observation. To 



