170 BPxITISH DESMIDIACE^E. 



Westmoreland. Cocket Moss, near Giggleswick and 

 Austwick Moss, W. Yorks ! Riccall Common, E. Yorks ! 

 Tliursley Common, Surrey ! 



WALES.- Bethesda and Capel Curig, Carnarvonshire ! 



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

 Forfar, Perth, Argyle, and Arran (Roy & Biss.). 



IRELAND.- -Donegal ! Galway ! Kerry! Sugar Loaf 

 Mountain, Cork (Arch.} Dublin and Wicklow (Arch.}. 



Geogr. Distribution. Germany. Switzerland. Austria. 

 Sweden. Bornholm. Finland. Poland (var.). N. Russia. 

 Faeroes. Greenland. Siberia. Mongolia. Patagonia 

 (var.). 



The characteristic spines and slightly incurved processes dis- 

 tinguish this species from all others. It is a frequent Desmid in 

 the western areas of the British Isles, although rarely seen outside 

 those districts. Archer reports the occurrence of different 

 combinations of 2, 3 or 4-radiate forms in the same individual. 



x 



Var. polyacanthum Nordst. (PL CXLIII, figs. 20-22.) 



St. oxyacanihum var. polyacanthum Nordst. Desm. Gronland, 1885, p. 11, 

 t. 7, f. 9 ; De Toni, Syll. Alg. 1889, p. 1219 ; Anders. Sverig. Chloroph. 

 1890, p. 12 ; Livtkem. Desm. Millstattersees, 1900, p. 23. 



Cells similar in form to the type, but larger, and with 

 slightly longer and rather more slender processes ; semi- 

 cells in front view with a number of scattered spines just 

 beneath the apex, sometimes occurring in two horizontal 

 series ; body of semicell with 2 or 3 short series of 



/ 



granules under each process. Vertical view usually 

 triangular, sides straight with about 2 parallel marginal 

 series of spines, spines numerous and sometimes scat- 

 tered; basal view of semicell with several short concentric 

 series of granules extending from the denticulations of 

 the processes to the isthmus, the innermost series being 

 larger and forming a concrescent verruca. 



Length 41-48 \i ; breadth, including processes, 59-68 ^; 

 breadth of isthmus 11-13 \L. 



ENGLAND. Austwick Moss, W. Yorks (N.C.). 



WALES.- -Llvn Ogwen, Carnarvonshire ! 



/' C? 



Geogr. Distribution. Austria. Sweden. Greenland. 



