TERMINOLOGY AND CLASSIFICATION OF DIATOMS. 97 



5. Classification adopted in this Work. 



As I have already stated above I have followed in this work the 

 classification of Professor H. L. Smith, which was published by its author 

 in 1872 in the Microscopical Journal The Lens, printed formerly at Chicago. 

 The conflagration, which shortly afterwards laid a large portion of that 

 city in ruins, also destroyed the greater portion of the edition of The 

 Lens. I attempted to supply this loss by publishing in 1878, in the third 

 edition of my treatise on the Microscope, a translation of Professor 

 Smith's work, made from a copy which my learned friend had the kind, 

 ness to forward me for my consideration, containing various corrections 

 and numerous additions intended to elucidate the original text. 



The classification of Prof. H. L. Smith is exclusively based on the 

 structure of the silicious epiderm or box. He regards ( r ) any classification 

 based upon the arrangement of the endochrome as simply impracticable, 

 as it is manifestly impossible to study many of the forms (e.g, those 

 of deep sea soundings and the various fossil deposits) with any regard 

 to this endochrome arrangement. He admits " that if only living 

 diatoms were available in every case, a system based on the endochrome 

 might be preferable, and in certain cases it would be easier to distinguish 

 the genus by the frustule, when living, than when mounted. Such is, for 

 example, the case in small Nitzschia. Since it is evident that the structure 

 of the frustule is, so to speak, co-ordinate with endochromatic arrange- 

 ment, and the former is permanent while the latter is transient, the 

 system which is based on the general build of the frustules cannot be 

 considered wholly artificial. Indeed in the parallel case of the animal 

 kingdom the two rival systems would be, one based on the position of 

 the viscera (scarcely this, as no organs are observed in the diatoms, and 

 so we may say distribution of the food), the other on the structure of the 

 skeleton. Few would hesitate which to choose." I have therefore in this 

 work followed the principal outlines of Professor Smith's classification, 

 but I have altered its details very considerably, since I regard them 

 from a slightly different point of view. 



The present work gives a description and figure of every genus 

 which is, in my opinion, at the present time admissible and of every species 

 generally distributed in the countries bordering on the North Sea. 



As already stated, all the original figures of this work have, as far 

 as possible, been drawn cr photographed at a magnification of 900 



( ' ) Notes on Cent. I. of the Species typicas Diatomacearum in the American Journal of 

 Microscopy for August, 1877. 



H 



