120 BRITISH DESMIDTACEJ1. 



semicell subcircnlar. Vertical view elliptic, with pro- 

 duced and submamillate poles, ratio of axes about 

 1 : 2*4. Cell- wall smooth. 



Zygospore unknown. 



Length 21 /u ; breadth 23 p.; breadth of isthmus 7 ^ 

 [Messrs. Roy and Bissett's figure measures 5 pJ] ; thick- 

 ness 9-9'4 p.. 



Geogr. Distribution.- -Gralicia in Austria. Poland. 

 East Greenland. Japan. Australia (var.). 



The typical form of this species is not known to occur in 

 the British Islands. 



Var. groenlandicum Borg. (PI. LXXI, figs. 19-21.) 



Cosmarium Capitulum Roy & Biss. var. groenlandicum Borg 1 . Ferskv. 

 alg. Ostgronl. 1894, p. 16, t. 1, f. 5 ; Freshw. Alg. Faeroes, 1901, p. 224; 

 West & G. S. West, Scott, Freshw. Plankton, I. 1903, p. 541, t. 15, 

 f. 5 ; Further Contrib. Freshw. Plankton Scott, Lochs, 1905, p. 500, 

 t. 7, f. 2-3 ; Comp. Study Plankton Irish Lakes, 1906, p. 85. 



Cells more robust with a broader isthmus; lower 

 half of semicells more inflated and semicircular ; 

 mamillate angles slightly reduced ; cell-wall punctate ; 

 vertical view broadly elliptic, with submamillate poles. 



Length 19-31/u,; breadth lG'4-25//,; breadth of 

 isthmus 7*7-1 1 *5 ^ ; thickness 11 '3-1 6 p.. 



SCOTLAND.- -In the plankton of Loch Morar, Inver- 

 ness!, Lochs Cuthaig and Roinebhall, Lewis, Outer 

 Hebrides !, and Loch Doon, Ayrshire ! 



IKELAKD.- -In the plankton of a small lake between 

 Clifden and Round stone, Gal way !, and in Lough 

 Caragh, Kerry ! 



Geogr. Distribution.- -Faeroes. Greenland. 



We have only observed this variety in the Scottish and 

 Irish plankton,, in which it is sometimes not uncommon. 



129. Cosmarium Corribense West & G. S. West. 



(PI. LXXV, figs. 6-8.) 



Cosmariwn Corribense West & Gr. S. West, Comp. Study Plankton Irish 

 Lakes, 1906, p. 101, t. 11, f. 20, 21. 



Cells small, about as long as broad, fairly deeply 



