TERMINOLOGY AND CLASSIFICATION OF DIATOMS. IOI 



evolution, i.e., genealogical descent ; and that it will be possible to 

 soundly appreciate the relative value of the forms of diatoms. 



At present we are only guided by personal appreciation and we are 

 describing and figuring many forms, which is certainly useful towards a final 

 enumeration and a perfect knowledge of the genealogical series. 

 But many of the present specific denominations have been created for 

 individual forms and for particular states and ought therefore to be 

 certainly curtailed. 



The difficulty is moreover very great, because no certain and really 

 fixed character exists for the delineation of speoies. The external outline, 

 size, striation, the smooth portions of the valve are all characteristics 

 which vary to a very considerable extent in examples of the same species, 

 and even the two valves may differ from one another, while age may 

 produce differences in their sculpture. 



However, the best authorities endeavour to greatly reduce the species 

 which it is really necessary to admit. Among these authorities figures 

 in the first rank the Honble. J. D. Cox, of Cincinnati, who published a short 

 time ago a work on this subject (*) which made a great stir amongst diatomists. 



Mr. Cox would reduce to seven forms the numerous species (many 

 hundreds !) of Coscinodiscus, even including in them Actinocyclus Ehrcnbergii. 

 These reductions have been severely criticised, as might be supposed, 

 but having received from the author a special copy of his work, 

 together with a number of photographs supporting his views, I am quite 

 of the opinion of the learned American diatomist that it would be very 

 advantageous to reduce the forms of Coscinodiscus to a small number 

 of species. It is, moreover, what I myself ventured to propose some 

 years ago in writing to many of my friends and it entirely accords 

 with the text of the Synopsis. Nevertheless, in my opinion, the genus 

 Adinocyclus ought to be kept separate. 



Up to the present time the only attempt that has been made to escape 

 from the labyrinth in which the diatomist thus finds himself, has 

 been but a limited one, viz : the study of pure gatherings, which are 

 unfortunately rare ; by the examination of the forms found in these 

 gatherings, their relations may sometimes be ascertained. 



We may now, however, expect to accomplish more in the future. 

 The cultivations originated by Dr. Miquel afford to the diatomist results 

 which he could not a short time ago have dared to hope for, 

 and it may well be anticipated that through the aid of these cultivations 



( *) " The Coscinodisceas." Notes on some unreliable criteria of genera and species, 1890. 



