144 THE ROYAL SOCIETY OF CANADA 



and has fewer bristles, turned outward from the angle between the 

 flat ends and the truncated edges. Th. siihtilis Ostend or what was 

 believed to be this species, was observed in only one instance, the 

 numerous small and four-angled structureless cells being united by 

 jelly into an irregular colony. Th. gravida Cleve has also, apparently, 

 been observed. 



COSCINOSIRA. 



Coscinosira polychorda Gran., of which only one specimen has been 

 observed, differs from Thalassiosira mainly in the fact that the con- 

 necting threads (slime organs) between the cells, are from four to nine 

 in number, instead of being single as in the last named genus. Peragallo 

 notes that Gran admits the structure of the frustule itself is that of 

 Coscinodiscus lineatus Ehr. which he admits as Forma polychorda; 

 but he has never seen the form living, and thinks it not sufficiently dis- 

 tinct to be noted as a variety, much less as a distinct genus. Gran, 

 however, considered it to be a genus neritic on the coasts of 

 northern Europe. 



LAUDERIA. 



Lauderia borealis Gran, is not uncommon in the plankton of 

 Vancouver Island. Chains of considerable length, but loosely con- 

 nected, are not unfrequently met with. Owing to imperfect silici- 

 fication the cells are apt to shrivel or become contorted during the 

 process of cleaning. The cell wall is marked by delicate transverse 

 bands. 



STEPHANOPYXIS. 



Specimens of Stephanopyxis, believed to be S. appendiculata 

 Ehr, have been rather frequently observed in the collections under 

 review, though they can hardly be said to be common. The rather 

 large size of the frustules with conspicuously areolated valves and the 

 crown of several bristles which separate or rather unite the frustules 

 into chains, readily attract attention. It is a species of wide distribu- 

 tion, being found alike in Europe, Africa, and North America. The 

 frustule of two valves when 40 microns in the direction of the chain 

 may be over 30 at right angles, each frustule being separated about 7 

 microns by the interlocked spines. 



CORETHRON. 



This genus is probably the most peculiar of all the plankton dia- 

 toms, sometimes presenting features which suggest a doubt whether 

 it is properly a diatom at all. In general shape, that of a lengthened 

 cylinder, it bears some resemblance to such forms as Rhizosolenia 



