236 Proceedings of the Royal Irish Academy. 



I was favoured with, the request of the Eoyal Irish Academy to 

 prepare a list of the forms to be met with in this country — a request 

 with which I unhesitatingly complied. Had I been content with 

 furnishing an inventoiy of the forms I had found, the task I had 

 undertaken might have been speedily performed ; but my anxiety was 

 to render the work as complete and as useful to my fellow- students as 

 I could, and as worthy of the reputation of the Eoyal Irish Academy 

 as it was possible for me to make it. "With this "^'iew I determined to 

 explore new localities, and to search more carefully, districts I had 

 previously examined. I was anxious also to avail myself of the 

 laboui's of the most distinguished authors on the subject, and was 

 therefore obliged to acquire a knowledge of languages with, which I 

 was previously unacquainted. 



Por all this, time was required, and I refer to the subject for the 

 purpose of showing that the long period that has elapsed since the task 

 was undertaken has been busily, and I hope not fruitlessly, occupied. 

 1^0 authentically named specimens were available ; and this proved to 

 me a soui'ce of much additional labour and delay. Those who ai'e 

 practically acquainted with the Diatomacese are aware how difficult it 

 is sometimes under the most favourable cii'cumstances to identify a 

 form. The difficulty is enhanced in cases in which the original 

 form, observed under the disadvantage of inferior instruments, has 

 been inadequately described ; and when a mistake has been made 

 in the figure or the description, the only satisfactory means of identifi- 

 cation is the inspection of the specimen. Hence some idea may be 

 formed of the difficulty and delay arising from the circumstance 

 of there being no authentic specimens preserved in any of the 

 Collections or Herbaria of Dublin. Many are the fiiends who have 

 kindly assisted me in the prosecution of this work, but special acknow- 

 ledgments on my part are due to Professor E. Perceval "Wright, M.D., 

 not only for the loan of collections but also of books and objectives, to 

 Eev. llaxwell H. Close, and A. Gr. llore, Esq., whose collections have 

 added numerous fonns to my list, as well as new localities for many 

 others ; and also to Dr. David Jloore, whose many and valuable 

 collections were kindly placed at my disposal. 



The name of BaciUariacese was employed to designate this group of 

 organisms at a time when little of their stmcture and habits, except 

 their outward form, was known ; and Pfitzer maintains that this desig- 

 nation should be retained because of its priority : but I have adopted 

 the more modern name of Diatomace£e, not only because it is more 

 pronounceable, but specially because it is more characteristic and more 

 generally known. 



The question, what is the proper position of the Diatomaceae in the 

 •classification of organized beings, has been variously answered. The 

 first known species were by their discoverers included amongst the 

 Confervacete ; the extraordinary movements, however, of Bacillaria 

 paxillifer, noticed by IT filler, induced that author to identify it with 

 the genus Yibrio ; and the position assigned to this form, as well as 



