154 BRITISH DESMIDIACEJE. 



ENGLAND.- -Near Ambleside (Archer) and plankton 

 of Easedale Tarn !, Westmoreland. 



WALES. Llyn Ogwen, Carnarvonshire ! 



SCOTLAND.- -Plankton of Lochs Shin, Ghriama, nan 

 Cuinne, and a Gharbh Bhaid Mhoir, Sutherland ! ; of 

 Loch Shiel, Inverness ! : of Loch Tay, Perth ! ; of Lochs- 

 Cuthaig, Fadaghoda, Stranabhat, an Sgath, and an 

 Tomain, Lewis, and Lochs Diracleet and Laxadale, 

 Harris, Outer Hebrides ! In bogs, Sutherland and Outer 

 Hebrides ! 



IRELAND. Connaught (Adams). 



Geogr. Distribution.- -Norway. Sweden. Finland. 

 LTnited States. 



This beautiful Desmid is a distinctly western type,* occurring 

 only in the region of the older and harder rocks in the western 

 parts of the British Islands. It is a general, but not abundant 

 constituent of Scottish plankton, and is also frequently found in 

 permanent Sphagnum bogs. The apical verrucae are subject to 

 considerable variation, being sometimes large smooth conical 

 nodules, and sometimes irregular lobed warts. 



Var. cambricum W. & C4. S. West. (PL CLII, figs. 3, 4.) 



St. Ophiura Cooke in Grevillea, 1880, t. 140, f. a-c : Brit. Desm. 1887, t. 59, 

 f. 1 (not descr. on p. 172) ; West, Alg. N. Wales, 1890, p. 18, f. 15. 



St. Ophiura var. cambricum West & G. S. West, New Brit. Freshw. Alg. 

 1894, p. 12. 



Cells about ll times broader than long, including the 

 processes, which are relatively shorter than in the type ; 

 apex of semicell more convex, with a circle of conical 

 nodules. 



Length 75-80 [i ; breadth, including processes, 98- 

 110[ji ; breadth of isthmus 16-18'5[JL. 



WALES. Capel Curig ! (Cooke < Witts) and in the 

 plankton, Carnarvonshire ! 



This variety differs from the type chiefly in its relatively 

 shorter processes. The conical nodules of the apex are found 

 occasionally also in the typical form instead of flattened verrucse, 

 and cannot be considered characteristic of var. cambricum. 



* See p. 18. 



