142 THE ROYAL SOCIETY OF CANADA 



by repeated washings. But not unfrequently there are with the Dia- 

 toms numerous microscopic Crustacea (Copepods, etc.), or it may be 

 Infusoria of different kinds ; and the removal of these presents greater 

 difficulties. The use of acids will remove calcareous organisms, but 

 is apt to separate the cells of concatenate species, or, if they are only 

 imperfectly silicified, to destroy them altogether. Probably the most 

 satisfactory method is the use of fine metallic screens, which will not 

 only filter off most of the Crustacea and Infusoria but may be employed 

 advantageously also in the separation of the larger from the smaller 

 species of Diatoms. 



After cleaning, the Plankton Diatoms may be examined either in 

 water or dry, when they are better seen than when mounted in balsam. 

 For the preparation and mounting of slides as well as for the recogni- 

 tion of many species we are indebted to Oliver Kendall, Jr., of Provi- 

 dence, R.I., U.S.A. In the determination of the species hereinafter 

 listed, reliance has been largely placed upon the publications of Dr. 

 H. H. Gran of Christiania, Norway, especially his contributions to 

 the "Nordisches Plankton" of Professors Brandt and Apstein in Kiel 

 (Leipzig, 1905); and again on the figures and descriptions in "Dia- 

 tomées Marines de France" of MM. H. and M. Peragallo^ and on 

 those of Dr. Henri Van Heurck's "Synopsis des Diatomées de Belgique." 

 Dr. A. Schmidt's "Atlas der Diatomaceenkunde," Wolle's figures, and 

 various special papers such as those of Brightwell on the Filamentous 

 and Long-horned Diatoms; the "Diatomaceen-typen-platte" of 

 about 400 species mounted by J. D. Moller of Wedel in Holstein, and 

 a thousand slides of named collections from over the whole world by 

 Professor J. Tempère of Paris were consulted. The average or ex- 

 treme dimensions of the species have been wholly determined by Dr. 

 A. H. MacKay of Halifax, Nova Scotia, and are noted briefly in the 

 general list according to a notation system there explained. 



CHAETOCEROS. 



This genus is by far the most abundant and most varied of the 

 typical Plankton Diatoms, and at the same time one of the most diffi- 

 cult to differentiate. Dr. Gran divides the species into two subgenera, 

 in the first of which (sub-genus Phaeoceros) the chromatophores are 

 equal in each cell and extend even into the bristles ; while in the second 

 {Hyalochaetae) these do not extend into the bristles which are filiform 

 or hairlike. To the first group belong Chaetoceros Peruvianum 

 Brightw., Ch. criophyllum Castr. and Ch. boréale Bails.; while the 

 others listed in the sequel belong to the second. 



Ch. decipiens CI. is one of the most common as also one of the 

 most conspicuous forms, and is easily recognized, partly by the large 



