48 BRITISH DESMIDIACEJ?. 



widely ; semicells broadly elliptical, dorsal margin 

 slightly convex, sometimes rather flattened on the 

 summit, ventral margin very convex, lateral angles some- 

 times slightly mamillate, furnished with a short spine 

 directed obliquely outwards, and with about 2 pairs of 

 spines projecting from the apical margin of each angle. 

 Vertical view usually triangular, sides straight, angles 

 acutely rounded, ending in a short spine, and with about 

 2 or 3 pairs of short spines on the apex in each angle, 

 directed outwards ; cell- wall punctate. 



Zygospore unknown. 



Length, without spines, 36-39 yL ; breadth, without 

 spines, 32-45 [i ; breadth of isthmus 15-19 [x. 



ENGLAND. --Hawkshead and Hampsfell. Lancashire ! 

 Strensall Common (IF. B. Turner) and Pilmoor, N. 

 Yorks ! Dartmoor, Devon (Harris). Cornwall (Marquand). 



WALES. Capel Curis; (Cooke & Wills) and Snowdon 

 (Roy). 



SCOTLAND. Sutherland, Ross, Inverness, Aberdeen, 

 Kincardine, Forfar, Perth, Argyle, Fife (Roy & Biss.}. 



IRELAND. Small lakes, Clifden to Roundstone, and 

 Derrvclare Lough, Co. Galwav ! Gleiwariff and Carran- 



/ / 



tu chill, Co. Kerry ! Dublin and Wicklow (Arch.}. 



Geoyr. Distribution.- -France. Germany. Galicia and 

 Austria. Hungary. Norway. Finmark. Sweden. Den- 

 mark. Bornholm. N. Russia. Faeroes. Spitzbergen 

 Greenland. Siberia. Japan. India. Turkey-in-Asia. 



73. Staurastrum oligacanthum Breb. 

 (PL CXXXIX, fig. 6.) 



>S7. oligacanthum Breb. Arch, in Quart. Journ. Micr. Sci. 1866, p. 67 and 

 p. 189 ; Nordst. Desm. Arctose, 1875. p. 36, t. 8, f. 39 ; Cooke, Brit. Desm. 

 1887, p. 145, t. 50, f. 8 ; De Toni, Syll. Alg. 1889, p. 1149 ; Roy & Biss. 

 Scott. Desm. 1893, p. 23 ; West & G. S. West, Alga-fl. Yorks. 1901, p. 98 ; 

 Comere, Desm. de France, 1901, p. 168, t. 12, f. 18. 



Cells small, about as long as broad, constriction fairly 

 deep, sinus acute, almost rectangular ; semicells de- 

 pressed hexagonal, apex truncate, lateral angles acute 

 and terminating in a conspicuous spine which is fre- 



