136 BRITISH DESMIDIACE^E. 



Plankton Irisli Lakes, 1906, p. 86 ; G-. S. West, Alg. Yan Yean, 1909, 



p. 28; W. & G. S. West, Brit. Freshw. Phytoplankton, etc., 1909, p. 181. 

 Didymidium (Staurastrum) muticum c. Bieneanum Reinsch, Algenfl. 



Frank. 1867, p. 151. 

 Staurastrum orbiculare (Ehrenb.) Menegh. var. Bieneanum Rabenli. Flor. 



Europ. Alg. Ill, 1868, p. 200. 

 St. muticum c. Bieneanum Kiabiii. in Bull. Soc. Imp. Natur. Moscou, 1888, 



no. 2, p. 329. 



Cells small, generally a little broader than long, very 

 deeply constricted, sinus widely open with an acuminate 

 apex ; semicells subelliptic, dorsal margin less convex 

 than the ventral margin and slightly flattened in the 

 middle, lateral angles subacute. Vertical view tri- 

 angular, angles subacute (or acutely rounded), sides 

 retuse in the median part. Cell-wall densely and finely 

 punctate. 



Zygospore globose, clothed with numerous, simple, 

 stout, slightly curved spines, which are a little dilated 

 at the base and sharp at the apex. 



Length 26-37'5/*; breadth 29-42^; breadth of 

 isthmus 7-9 ^ ; diam. zygosp. without spines 33-35 /^, 

 with spines 50-52 p,; length of spines 8-10 p. 



ENGLAND.- -Borrowdale, Cumberland! Brothers' 

 Water, Westmoreland ! Pilmoor, N. Yorks ! Epping 

 Forest, Essex ! Goring, Oxfordshire (with zygospores) ! 

 New Forest, Hants ! 



SCOTLAND.- -Loch Hempriggs and St. John's Loch, 

 Caithness ! Kerloch and Blackball, Kincardine ; Bal- 

 quhadly in Fern, Forfar (Roy fy Bissctt). Benbecula, 

 Outer Hebrides ! Orkneys ! Plankton of Loch Bair- 

 ness, Inverness ! Plankton of Lochs Cuthaig, Fada- 

 ghoda, Roinebhal, and an Tomain, Lewis, Outer 

 Hebrides ! 



IRELAND.- -Lough Cloncarney and Sproule's Lough, 

 Donegal ! Creggan Lough, Galway ! Upper Lake of 

 Killarney, Kerry ! Adrigole, Cork ! Plankton of 

 Loughs Caragh and Currane, Kerry ! 



Geogr. Distribution.- -Germany. Austria. Norway. 

 Sweden. Bornholm. Faeroes. Nova Zembla. Russia. 

 Siberia. Japan. Si am (var.) New Zealand. Mada- 

 gascar. E. Africa (var.). United States. 



