INTRODUCTION. 



In scarcely any department of natural history is the synonymy so intricate as in that of 

 the Diatomaceoe. An enormous number of names has been given to forms, frequently very incom- 

 pletely described, or not at all, and often inaccurately iigured. Moreover the literature is scattered 

 throughout papers and periodicals, in many different languages, some of which are of very diifii- 

 cult access. These circumstances, together with the necessity of using the most excellent and 

 powerful lenses, make the study of the diatoms a difficult one. But that study is of considerable 

 importance. These small organisms form a peculiar class of highly developed unicellular algse, the 

 structural investigation of which may bring to light facts of much interest. Their silicious shells 

 are very persistent and occur in a fossil state in strata of clays, marls, limestone etc., belonging 

 to different geological epochs, especially the tertiary and post-tertiary, and may become of great 

 value in geological researches, as certain indications of the nature of the water in which the sedi- 

 ments were deposited. When carefully studied the fossil diatoms will surely become as important 

 as the fossil shells. Such considerations induced me six years ago to subject the Diatomacese to a 

 critical examination, with the principal objects of getting rid of the heavy burden of names of slight 

 or obscure import, of limiting as concisely as possible the genera or groups, species and varieties, and 

 of classing them according to their natural relations. Every one who knows the amount of lite- 

 rature in the diatomology must be aware that such an enterprise would occupy an ordinary life 

 time, or at any rate a large part of it. It was therefore necessary to limit the work to some di- 

 vision of the diatoms. The large and beautiful discoid forms have attracted many workers, and 

 have been described in numerous monographs ; but less interest has been bestowed on the RaphidieEe, 

 which are of more importance in the geological researches of my country. I have, then, preferred to 

 limit my present work to the Raphidiese which are characterised by the presence of a median line, 

 a feature of their valves which must be of great importance, to judge from its constant occurrence 

 in this tribe. 



For the complete knowledge of these diatoms it would have been desirable to study them 

 in the living state, and complete the splendid work in this direction begun by Pfitzbr; but I had 

 very little time for such researches, the examination of many thousand slides, and drawings of almost 

 all the forms having occupied me principally, and prevented me from a more extensive study of the 

 living forms. My principal object was to construct a solid basis for farther researches in different 

 directions, and in my opinion the iirst thing to be done was to systematize the nomenclature so as 

 to make it possible to recognize the forms registered in the science. In the following synopsis I 

 have endeavoured to give as exact diagnoses as possible of all forms, belonging to the tribe Ra- 

 phidieee, not omitting any one described or figured heretofore in a manner to be recognized. I there- 

 fore propose that all names, • not mentioned here, may be dropped in oblivion. To give a list of 

 all those names of doubtful or obscure signification would be a very fruitless work, but if any of 

 my readers desires to search for such, he will find them set forth in the catalogues of Habirshaw 

 and of Chase or in the large work recently published by De Toni (Sylloge algarum Vol. II Ba- 

 cillariese Sect. I Raphidiese) in which he has given diagnoses of or at least mentioned all the pu- 

 blished forms. In the last named work also a very valuable list is supplied of publications on the 

 diatoms, prepared by Dbby, which relieves me from the necessity of giving such a list here. 



