PREFACE. 



state at length the views of foreign authors, merely to show in 

 what respects I differ from their conclusions, or to detail their 

 systems only to illustrate my own departures from their methods 

 of arrangement, appeared to me less likely to serve the cause of 

 a branch of knowledge yet in comparative infancy, than to place 

 before the inquirer a series of observations for which I could 

 personally vouch, and thus to accumulate facts, at present so 

 scantily supplied, upon which the future student might rest a 

 more complete structure of theory and classification. 



How far the present work contains materials new to the 

 English reader will be understood when I state, that of the 224 

 species included in the first sub-tribe, not more than twenty have 

 hitherto been recorded by our native observers ; and of the others, 

 a very large proportion are either for the first time described, or 

 can only be doubtfully referred to the outline figures given by 

 Ehrenberg and Kiitzing, and rendered accessible to the Enghsh 

 reader in the pages of Pritchard's History of Animalcules. 



But the task I had assigned to myself would have been much 

 less productive of results had I not been aided by the frank and 

 cordial co-operation of fellow-inquirers, who, by the liberal com- 

 munication of specimens from other localities, have enabled me 

 to enrich my record with some of its most beautiful and inter- 

 esting forms. It is my pleasing duty to acknowledge the obli- 

 gations I thus owe to Mrs. Griffiths of Torquay, Dr. Dickie of 

 Belfast, Dr. Greville of Edinburgh, Professor Williamson of Man- 

 chester, Mr. Edward Jenner of Lewes, and M. De Brebisson of 

 Ealaise, whose entii-e herbaria in some cases, or in others ample 

 selections therefrom, as far as relates to the Diatomacese, have 

 been placed at my command. I have, however, to regret that 

 these collections, with one exception, contain but few species in 

 the genera embraced in my first volume, and that in this ex- 

 ception, Avhich refers to the species from Ealaise, the specimens 



