144 BRITISH DESMIDIACEJE. 



Geogr. Distribution. France. Germany. Austria 

 and Galicia. Norway. Sweden. Bornliolm. X. and 

 S. Russia. Faeroes. Greenland. United States. 



The species is well characterized by the outward form of 

 the semicells, the open sinus and broad isthmus, as well as by 

 the large, scattered scrobiculations in the centre of the semi- 

 cells. 



9. Cosmarium ocellatum Eichler & Gutw. 

 (PL LVIII, fig. 6.) 



Cosmarium ocellatum Eiclil. & Gutw. Norm. Spec. Alg. Nov., 1894, p. 164, 

 t. 4, f. 7. 



Cells small, 1-g 1J times as long as broad, deeply 

 constricted, sinus linear and dilated towards the apex ; 

 semicells subsemicirciilar-pyramidate, basal angles and 

 apex rounded. Side view of semicell subcircular. 

 Vertical view elliptic, ratio of axes about 1 : 2*25. 

 Cell-wall smooth or very finely punctate, with a large 

 scrobiculation in the centre of the semicells. Chloro- 

 plasts axile, each with one pyrenoid. 



Zygospore unknown. 



Length 20-30 /x; breadth 17-23^; breadth of 

 isthmus 4-6 ^ ; thickness 9-14 //,. 



Geogr. Distribution.- -Q&licia in Austria. 



The typical form of this species has not yet been observed 

 in the British Islands. 



Yar. incrassatum West & G. S. West. (PL LVIII, 



fig. 7.). 



C. ocellatum var. incrassatum West & G. S. West, Alg. S. England, 1897, 

 p. 485, t. 6, f. 12. 



A variety with the sinus always open ; semicells with 

 subtruncate apices. Cell-wall in the centre of the 

 semicells with a thickened area of a yellowish colour, 

 containing a small central scrobiculation surrounded 

 by 2-5 smaller ones. Vertical view elliptic, with a 

 slight, flattened protuberance at the middle on each 

 side. 



