146 THE ROYAL SOCIETY OF CANADA 



face it resembles B. Tuomeyi Bail, found at Campeachy Bay, Cal., 

 and may be a variety of that species. 



TRICERATIUM. 



This genus is by Gran, Albert Mann and others regarded as in- 

 separable from Biddulphia, except as regards a few forms referred by 

 Cleve to a new genus, Trigonium. I have preferred here to retain the 

 old name, at least as regards the three-angled forms. Of these the 

 old and wide-spread Tr. alternans Ehr. is fairly common in the Van- 

 couver collections; while with it but less common is a much larger 

 species having small aréoles radiating from the centre, with large va- 

 cant spaces at the angles. Some instances have also been observed 

 of a quadrangular form (by some known as Amphitetras Ehr.) with 

 large pentagonal areolations and punctate angles. 



Finally, forms occur resembling the Tr. undulatum of Brightwell, 

 but these seem to be identical with Ditylum Brightwellii as figured by 

 Gran, being enclosed in a cylinder and armed at either end with a long 

 stout central bristle. The fact that such cylinder sometimes contains, 

 even in a single cell, triangular, quadrangular and pentagonal frus- 

 tules, goes far to justify the view that all these shapes are varieties of 

 a single polymorphous genus. 



COSCINODISCUS. 



Though one of the most frequently occuring Diatoms in plank- 

 ton collections, species of Coscinodiscus are not remarkedly abundant 

 in the gatherings from Vancouver waters, at least about Nanaimo. 

 Not less than 22 species, however, have been recognized, as given in a 

 subsequent list. Of those named there C. excentricus Ehr. is perhaps 

 the most common but the smallest; while C. concinnus Sm. is prob- 

 ably the largest. This species can usually be recognized not only by 

 its large size, but by the fineness and closeness of its markings, and 

 usually by the occurrence of a submarginal area traversed radially by 

 short radial fine lines. A central umbilical rosette may or may not be 

 present according as it is the upper or lower valve which is visible. 

 Another large form, marked by a central rosette is C. aster omphalus 

 Ehr., a very widely distributed species which is regarded by some 

 authorities as only a variety of C. oculus-iridis Ehr. 



ARACHNODISCUS. 



This is one of the most beautiful diatoms to be found on the Pacific 

 coast, where it is often found sessile on the fronds of algae, and is, 

 therefore, not strictly planktonic. Several specimens have been 



