114 BRITISH DESMIDIACE^;. 



and Thursley Commons, Surrey ! Roughter Moor, 

 Cornwall ! 



SCOTLAND.- -Ross, Inverness, Aberdeen !, Kincardine, 

 Perth !, Argyle (Roy $ Bissett). Sutherland ! Lewis, 

 Outer Hebrides ! 



IRELAND.- -Near Grlenties and Lough Anna, Donegal i 

 Dublin and Wicklow (Archer) . Ballynahinch, Gralway I 



Geor/r. Distribution.- -France. Germany. Switzer- 

 land. Austria and Galicia. Sweden. Bornholm. 

 Poland. Greenland. Japan. Azores. United States. 



This minute species is rather rare and liable to be over- 

 looked. Its characters are most distinctive, and it cannot 

 easily be confused with any other species of the genus. 

 Lundell gives measurements of Swedish specimens up to 18 /* 

 in length and breadth. 



Var. truncatus West, (PI. CXYII, fig. 14.) 



A. bifidus Breb. var. truncatus West, Alg. N. Yorks. 1889, p. 293, t. 291, 

 f. 9; Alg. W. Ireland, 1892, p. 169; Alg. Engl. Lake Distr. 1892, p. 

 730; Alg. S. England, 1897, p. 496; Alga-fl. Yorks. 1901, p. 109; 

 Alg. N. Ireland, 1902, p. 57. 



Semicells subhexagonal, sides and apex straight ; 

 " angles ' not emarginate but truncate, thus making 

 two angles (lateral and apical) on each side of the 

 semicell, each angle being furnished with a minute 

 spine. 



Length (including minute spines) 10-1 5' 5 p, ; breadth 

 10-14*4 jit ; breadth of isthmus 4*5-5*7 ft. 



ENGLAND.- -Bowness and Helvellyn, Westmoreland ! 

 Strensall and Pilmoor, N. Yorks ! Thursley Common, 

 Surrey ! Keston Common, Kent ! 



WALES.- -Moel Siabod, Carnarvonshire ! 



IRELAND. --Near Grlenties, Donegal ! Ballynahinch, 

 Lough Derryclare, and in small lakes between Clifden 

 and Round stone, G-alway ! 



Although distinctly rare, we have seen this variety oftener 

 than the type, from which it differs most markedly in the 

 angularity of its semicells. 



One form of it was observed from Bowness, Westmoreland, 

 in which the semicells were entirely destitute of spines. 



