PREFACE. Vll 



reached ine at so late a period that I have been unable to use 

 them in the nomenclature of my plates, and could only employ 

 them in correcting and enlarging the synonyms given in the text. 



For other specimens, and many of them in a living state, I 

 am indebted to gentlemen, whose favours I have recorded under 

 the species they have respectively contributed. Among these 

 fellovr-labourers I must not omit a special acknowledgment to 

 my zealous and indefatigable correspondent Chr. Johnson, Esq. 

 of Lancaster, who, by frequent communication of specimens col- 

 lected by himself and Mr. George Smith of Wray, and by the 

 liberal aid of books and translations, has contributed important 

 assistance. 



Nor do I wish to leave unnoted the labours of my predecessors, 

 more especially those of Mr. Ralfs and Mr. Thwaites, to whom 

 is due nearly all that has been known of our British species of 

 Diatomacese. How much is owing to the acciu'ate and laborious 

 researches of Mr. Ralfs, will be better seen in my second volume, 

 which will embrace the greater number of the genera to which 

 he has directed his attention. 



I have, lastly, to acknowledge the efficient assistance received 

 from my able coadjutor Mr. Tuffen West, whose accurate re- 

 presentations, in every case faithfully drawn from nature, have 

 so materially enhanced the value of my work to the scientific 

 student, and conferred upon it much of whatever value it may 

 possess, in the estimation of the general observer. 



As I have not admitted anything into my pages which I have 

 not verified by actual observation, I have abstained from re- 

 cording localities unless specimens have been seen and examined 

 by myself. In the uncertainty which attended the nomenclature 

 of species, and the imperfect means of identification open to the 

 English observer, this course was imperative. 



I have departed from the rule in one case only, Araclmoidiscus 



