144 BRITISH DESMIDIACE^E. 



semicell. There is a strong resemblance between the small form 

 and var. longibrachiatum West (see PL CXLVII, fig. 5), and yet 

 it is strange that the two were not considered identical by the 

 Wests, who listed PL CXLVII, fig. 1 as typical St. anatinum. 



St. anatinum is a very handsome Desmid, which, although 

 widely distributed in the British Isles, is only really abundant 

 in North Wales, the west of Ireland, and the north-west of 

 Scotland. Thus it is more frequently found in bogs and in the 

 plankton of lakes lying on the older palaeozoic rocks, although it 

 is not exclusively confined to such localities. This fact rather 

 explains its occurrence in Norway and Sweden (where the 

 geological formation is similar to that of the western parts of 

 the British Isles), although it has not yet been recorded for the 

 greater part of continental Europe. It is one of the most 

 characteristic Desmids of Welsh, Scotch and Irish plankton. 



Var. grande W. & Cl. S. West. (PL CXLVII, fig. 6.) 



St. anatinum var. grande West & G. S. West, Alg. N. Ireland, 1902, p. 55, 

 t. 1, f. 27 ; Scott. Freshw. Plankton, I, 1903, p. 530 ; Further Contrib. 

 Plankt. Scott. Lochs, 1905, p. 504. 



Cells larger than in the type, with, the processes 

 slightly longer. 



Length, without processes, 66 \i ; with processes, 

 105-112 [i ; breadth, with processes, 140-148 p ; breadth 

 of isthmus 15'5 \L. 



WALES.- -In the plankton. 



SCOTLAND.- -Rhiconich and in the plankton of Loch 

 Shin, Sutherland ! Plankton of L. Shiel, Inverness ; 

 of Loch Doon, Ayr ; of Loch Fadaghoda and 5 other 

 lochs in Lewis and Harris, Outer Hebrides ! 



IRELAND. Lough Anna, Donegal ! 



This variety is one of the most handsome of all Staumstm. 

 It is more abundant in plankton than in any other situation. 



Var. Lagerheimii (Schmidle) W. & G. S. West. (PL 



CXLVII, fig. 4.) 



St. Lagerheimii Schmidle, Lappmark Siisswasseralgen, 1898, p. 03, t. 3, f. 10. 

 St. Landmarkii Huitfeldt-Kaas, Plankton Norske Vande, 1906, p. 155, t. 2, 



f. 32, 33. 

 St. anatinum var. Lagerheimii, West & G. S. West, Plankton Engl. Lake 



Distr. 1909, p. 289. 



