252 BRITISH DESMLDIACEJ5. 



6. Desmidium coarctatum Nordst. 

 (PI. CLXV, figs. 1, 2.) 



De&midium (Didymoprium) coarctatum Nordst. Botan. Notiser, 1887, p. 155. 

 D. coarctatum Nordst. Freshw. Alg. N. Zealand, 1888, p. 25, t. 2, f. 3 ; De 



Toni, SylL Alg. 1889, p. 785 ; Borge, Austral. Susswasserchl. 1896, p. 8 ; 



W. & G. S. West, Some N. Ainer. Desin. 1896, p. 233 ; Nordst. Index 



Desm. 1896, p. 76 ; W. & G. S. West, Desm. U. States, 1898, p. 321, f. 7 ; 



Freshw. Alg. Ceylon, 1902, p. 194 ; Playfair, New S. Wales Census, 1917, 



p. 240. 



Filaments flattened, twisted, cells in front view ellip- 

 tical, about li times broader than long, with a slight 

 median constriction, sinus linear, basal angles of semi- 

 cell acutely rounded, lateral margins slightly undulate ; 

 apex of semicell about -i- its diameter ; lateral view of 

 cell quadrangular, with the faintest indication of a 

 median constriction ; vertical view narrowly elliptical 

 with prominent rounded mamillse at the opposite 

 poles. Cell- wall with longitudinal rows of minute 

 punctse ; chloroplasts axile, one in each semicell, each 

 with a central pyrenoid. 



Zygospore unknown. 



Length 25-34 \L ; breadth 34-38 fji ; breadth of isth- 

 mus 33 [L ; breadth of apex 12-14 ^ ; thickness 24-26 JJL. 



Geogr. Distribution.- -Finland. Ceylon. Australia. 

 New Zealand. United States. 



Var. cambricum. (PL CLXV, figs. 3, 4.) 



D. coarctatum var. cambricum West, Alg. N. Wales, 1890, p. 7, f. 2 ; W. 

 & G. S. West, Further Contr. Plankt. Scott. Lochs, 1905, p. 505, t. 4, 

 no. 5, f. 1. 



Differs from the type in its different proportions and 

 in the broader apices of the cells. 



Length 22 '5 \L ; breadth 40-45 y. ; breadth of isthmus 

 35-37'5 LI ; breadth of apex 17'5-20[Ji ; thickness 32- 



WALES. Capel Curig, Carnarvonshire ! In the plank- 

 ton ! 



SCOTLAND. Plankton of Loch Fadaghoda, Lewis, 

 Outer Hebrides ! 



