ii THE VOYAGE OF ELKS. CHALLENGER 



Jlooker, I was informed by the late Sir "Wyville Thomson that everything would be done 

 to aid this investigation. The announcement which I received somewhat later from Mr 

 John Murray that Sir Wyville Thomson proposed that I should undertake a systematic- 

 examination both of the littoral and pelagic Diatoms brought home by the Expedition 

 caused me no little delight or surprise. The proposal, however, I gladly accepted, and 

 although conscious of the arduous nature of the work, I resolved to spare no pains in 

 making it as complete as the time at my disposal would permit. 



The materials as intrusted to me consisted of about a hundred small bottles con- 

 taining muds or oozes from different regions, together with several surface collections 

 obtained by the use of the tow-net. The whole was in excellent condition, and the 

 depth and position of the gathering, as well as the date when it was procured, were 

 carefully recorded on every sample. 



The time necessary for the preparation of illustrative slides from so many gatherings 

 and for the determination of new genera and species has necessarily been somewhat long, 

 but I am indebted to Mr Murray for an extension, more than once, of the period at first 

 "ranted to me, and this has enabled me to make the present Report somewhat more 

 complete than it otherwise could have been. It cannot be doubted, however, that 

 .among the great amount of material at my command many new or rare forms have 

 escaped observation, and these may be published at a subsequent time as a supplement 

 to the present work. 



In several cases criticisms have been offered or emendations given of the definitions 

 of previously known genera and species. As was to be expected from the examination 

 of gatherings made in so many hitherto unexplored regions, the list of new species that 

 have been established — some provisionally — is considerable, but care has been taken to 

 limit these as far as possible. A few new genera have been founded, but on the other 

 hand several old ones have been abolished, our recent advances in the knowledge of the 

 Diatomaceaa being such as to reveal the inadequacy of the characters that have been 

 hitherto regarded as of generic value. In all cases where the differences between any 

 form and the already known typical species have been of a subordinate kind and quite 

 insufficient to justify the introduction of new specific names, varieties have been consti- 

 tuted, but these instances are not very numerous. 



Although in the earlier stages of my work it was my endeavour to record the various 

 species that occurred in each gathering with a view of perfecting somewhat more fully 

 our knowledge of the environments and geographical distribution of the various species, I 

 soon abandoned this method, and have been satisfied by merely recording in most cases 

 the locality from which the various species described have been obtained. 



The plates have been prepared under my direct supervision by Signor Cesare Cerri, 

 and to him my best thanks are due for the faithful manner in which he has executed the 

 work. It is perhaps somewhat unfortunate that a natural classification has not been 



