146 BEITISH DESMIDIACE^E. 



Cells rather under medium size, about as long as 

 broad, deeply constricted, sinus open and acute-angled, 

 very narrow at the extremity ; semicells oblong-elliptic, 

 ventral margin frequently more convex than dorsal 

 margin, apex convex, subtruncate,or sometimes slightly 

 retuse in the middle, lateral angles rounded and fur- 

 nished with a small mucro or papilla. Vertical view 

 triangular, with concave sides and rounded angles, 

 each anle furnished with a small mucro. Cell-wall 



smooth. 



Zygospore unknown. 



Length 27-50 ^ ; breadth 27-49 p.; breadth of 

 isthmus 8-1 7 ju. 



ENGLAND.- -Westmoreland ! (Bissett). Hawkshead 

 and Hampsfell, Lancashire ! Malham Tarn, "W. Yorks ! 

 Gormire and Pilmoor, N. Yorks ! Riccall Common, 

 E. Yorks ! Thursley Common, Surrey ! Sussex 

 (Rolfs). New Forest, Hants ! (Roif). Cornwall 

 (Ralfs). 



WALES. Capel Curig, Carnarvonshire ! Plankton 

 of Llyn Ogwen ! 



SCOTLAND. --Sutherland, Inverness !, Aberdeen, Kin- 

 cardine, Forfar, Perth (Roy fy Bissett). Plankton of 

 Loch Shiel, Inverness ! Loch Stranabhat, Lewis, 

 Outer Hebrides ! Plankton of Shetlands ! 



ICELAND.- -E. of Glenties, Donegal ! Plankton of 

 lakes in Mayo, Gal way, and Kerry ! Dublin and 

 Wicklow (Archer). Plankton of Loughs Neagli and 

 Beg ! Lough Fea, Londonderry ! 



Geogr. Distribution.- -France. Germany. Switzer- 

 land. Austria and Galicia. Hungary. Macedonia. 

 S.ervia. Italy. Norway. Sweden. Denmark. Born- 

 holm. Poland. N. Russia (var.). Iceland. Green- 

 land. NovaZembla. Siberia. India. Abyssinia (var.). 

 Central Africa. United States. Paraguay. Patagonia. 



St. brevispinum is a well-marked and widely distributed 

 species. It is distinguished from St. aversum by the shape 

 of the semicells and the sinus, the latter being almost 

 mucronate at the extremity. The short papilla3 at the angles 



