Author's Preface. 



The Synopsis, the last part of which was published in 1S85, had 

 the good fortune to meet with so favourable a reception by diatom- 

 philes that the work was promptly subscribed, and, in consequence, its 

 selling price increased considerably. 



Its present enhanced value, and the fact that only a few copies 

 are now available, prevents all but those with considerable means from 

 acquiring it. 



Under these circumstances it has occurred to the Author that it 

 would be useful to publish a work, in some respects more limited, and 

 at such a price as to be within the reach of all persons of average 

 means. 



The scope of the present Treatise includes all the information of 

 which we can be certain concerning the Life History and Structure 

 of Diatoms. 



It also comprises a description of every genus that can with reason 

 be admitted at the present time, as well as of every species that has 

 been hitherto found in the North Sea, and of those more commonly 

 found in the countries abutting thereon, viz. : Great Britain, the extreme 

 north of France, Belgium, Holland, Denmark and Norway. 



Under these conditions it is hoped that the Work will be found 

 useful, not only to those who merely devote themselves to a general 

 and summary examination of diatoms, but also to those who desire to 

 determine the species found within this area. 



It is essential that a book of this nature, to attain its object, should 

 contain a large number of figures ; and, consequently, although as many 

 Synopsis-figures as possible have been made use of, several hundred 

 others have been added. The fact that all these have been reproduced 

 on a moderate scale by the process of phototypography, has enabled 

 greater clearness to be attained than in the Synopsis, whilst keeping 

 the price within moderate limits. 



