190 BRITISH DESMIDIACE^E. 



SCOTLAND. General ! zygospores from Dinnet, Aber- 

 deen (Roy & Biss.). Orkneys ! Not uncommon in the 

 plankton of Loch Morar, Inverness, Loch Tay, Perth, 

 and Lochs Fadaghoda and an Tomain, Lewis, Outer 

 Hebrides ! 



IRELAND. Mayo ! Gal way, and in the plankton of 

 Lough Corrib ! Kerry ! Plankton of Lough Neagh ! 

 Dublin and Wicklow (Arch.). 



Geogr. Distribution.- -France. Germany. Switzerland. 

 Galicia and Austria. Hungary. Servia. Italy. Norway. 

 Sweden. Denmark. Bornholm. Finland. Poland. 

 Faeroes. Iceland. Greenland. Siberia. Mongolia. 

 United States and Alaska. Yukon. Nova Scotia. 

 Patagonia. 



St.furcigemm is a very common species often found in quantity 

 in pools amongst Myriophyllum, Sphagnum or Utricularia. It 

 is also a general constituent of the plankton of British lakes. 

 The upper whorl of processes is liable to variation, and tran- 

 sitional forms between the type and forma eustephana are not 

 infrequent (vide infra). 



Forma eustephana (Ehr.) Nordst. (PI. CLVII, fig. 1.) 



Desmidium eustephanum Ehr, Micr. Leb. S. & N. Amer. 1843, p. 124, t. 4, 

 f. 23. 



Staurastrum eustephanum Ralfs, Brit. Desm. 1848. p. 215 ; Arch, in Pritch. 

 Infus. 1861, p. 742, t. 2, f. 3 ; Rabenh. Flor. Europ. Alg. 1868, p. 220 ; 

 Wolle, Desm. U. S. 1884, p. 147, t. 48, f. 9, 10 ; Cooke, Brit, Desm. 1887, 

 p. 177, t. 62, f. 2 ; West, Desm. Massach. 1889, p. 6, t. 3, f. 18 ; De Toni, 

 Syll. Alg. 1889, p. 1223, West, Alg. N. Wales, 1890. p. 19 ; Alg. W. Ireland, 

 1892, p. 185 ; Roy & Biss. Scott. Desm. 1893, p. 19 ; West & G. 8. West, 

 Alg. S. England, 1897, p. 496 ; Cushman in Bull. Torr. Bot. Club, 1905, 

 p. 228, t. 8, f. 19. 



Stephanoxanthium eustephanum Kiitz. Spec. Alg. 1849, p. 184. 



Staurastrum furcigerum forma eustephana Nordst. Bornholm Desm. 1888, 

 p. 207 ; G. S. West, Variation Desm. 1899, p. 396. 



This form only differs from typical St. furcigerum in 

 that the upper whorl of processes is doubled, consisting 

 of 6 instead of the usual whorl of 3 in the ordinary 

 triradiate specimen. The lower processes are quite 

 normal. 



Length, without processes, 40 [JL ; including processes, 

 58 pi ; breadth, including processes, 57 (JL ; breadth of 

 isthmus 12 i. 



