148 THE ROYAL SOCIETY OF CANADA 



resembles A. undulatus in its ordinary form, but of the six segments 

 three alternate ones are marked by conspicuous prominences or um- 

 bones, something like those of Aulacodiscus but smaller. The other 

 differs from the ordinary form in some respects and is ten-rayed. 

 It may prove to be one of the numerous varieties of A . undulatus. 



ACTINOCYCLUS. 



This genus is represented by at least one species. A. suhtilis 

 Ehr. The surface of the circular valve is marked by two sets of 

 radiating lines of which one is very fine and closely approximated, 

 while the other consists of more conspicuous dots or bars which are 

 widely separated. The species are often irridescent under medium 

 high powers when slightly out of focus. 



ASTERIONELLA. 



Representatives of this genus are occasionally met with but the 

 identity of the species is not easily determinable. Forms bearing a 

 close resemblance to Ast. Japonica CI. have been observed, the inner 

 part of each cell broad and somewhat triangular, and from the base 

 gradually and continuously narrowing to the obtuse extremity. Others 

 have been referred by Dr. MacKay to Ast. formosa Hassell. var. 

 near Ast. Bleakeleyi Sm., and doubtfully to Ast. notata Grun. 



DITYLUM. 



Forms believed to be referable to the genus Ditylum Bailey 

 are met with in the collections from Vancouver Island sometimes in 

 large numbers. One has the general shape of D. Brighlwellii Grun. 

 as figured by Gran, viz.: that of a cylinder somewhat puckered at 

 either end and having at the ends long stout central bristles ; but instead 

 of the surrounding crown of fine hairs, single small bristles project 

 obliquely outwards from either angle of the cell. Another and still 

 more doubtful form has the sides of the cylinder in the shape of two 

 sigmoid lines which intersect each other opposite the middle of the 

 cell, and at their extremities are extended into short recurved spines 

 on either side of a central stout spine. Only one specimen of the latter 

 has been seen. 



ACHNANTHES. 



Seven species of this genus have been observed of which the most 

 common are A. longipes Ag. and A. suhsessilis Ktz. Some doubtful 

 varieties were thought to be observed occasionally. 



