12 BRITISH DESMIDIACE^;. 



diam. zygosp., without spines, 33'7 JJL ; length of spines 

 12-5 p. 



ENGLAND.- -Wastdale, Cumberland ! Helvellyn and 

 near Bowness, Westmoreland (Biss.). Cullingworth 

 and near Settle, W. Yorks ! Mickle Fell and Pilmoor, 

 N. Yorks ! Risley Bog (Roy] and Hampsfell, Lanca- 

 shire ! Leicester (Roy). Enbridge Lake, Hants (Roy). 

 Keston Common, Kent ! 



WALES. Capel Curig, Carnarvonshire ! 



SCOTLAND. General, but scarce (Roy & Biss). 



IRELAND.- -Lough Gartan, Donegal ! Dublin and 

 Wicklow (Arch.). 



Geogr. Distribution.- -France. Germany. Galicia in 

 Austria. Roumania. Norway. Sweden. Bornholm. 

 Poland. Spitzbergen. Siberia. N. India. United 

 States. Alaska. 



This species is not quite as common as St. dejectum, to which 

 it is very closely allied. It is distinguished from the latter by 

 its more convex apex and elliptical semicells, whilst its laterally 

 inserted spines, which are rather small, are either parallel or 

 more rarely slightly converging. In St. dejectum the semicells 

 are cuneate rather then elliptic. 



Var. subtriangulare West & G. S. West. (PL CXXX, 



figs. 13, 14.) 



St. mucronatum var. subtriangulare W. & G. S. West, Scott. Freshw. Plankton, 

 I, 1903, p. 545, t. 17, f. 11 ; Freshw. Alg. Burma, 1907, p. 213, t. 15, 

 f. 20 ; Borge, Botan. Notiser, 1913, p. 28. 



Cells rather larger than in the type, the sinus more 

 widely open ; dorsal margin of semicell nearly straight 

 or slightly convex, ventral margin nearly semicircular. 



Length 26-44 (JL ; breadth, without spines, 29-44 pi ; 

 length of spines 3'8-4'6(ji ; breadth of isthmus 6-13 (JL. 



ENGLAND.- -Plankton of Grasmere, Westmoreland ! 



WALES.- -In the plankton ! 



SCOTLAND. --Plankton of Loch Doon, Ayrshire ! 



Geogr. Distribution. Sweden. Finland. Burma. 



