STAURASTRUM. 137 



St. Bieneanum, originally described by Rabenhorst as a 

 distinct species, was subsequently placed by that author as 

 a variety of St. orbiculare (Ehreiib.) Kali's. It cannot be 

 considered as a near relative of the latter species, however, 

 and throughout the British Islands it maintains its characters 



O 



very constantly. The lower margins of the semicells are 

 always more convex than the upper ones, an inequality of 

 curvature which causes a slight outward divergence of the 

 semicells. The dorsal margin is always truncate or faintly 

 retuse in the middle, the angles of both front and vertical 

 views are subacute, and the cell-wall is delicately but dis- 

 tinctly punctate. The zygospores possess fewer, shorter, and 

 stouter spines than those of St. orbiculare var. Ralfsii. 



Forma spetsbergensis Xordst. (PI. CXX, fig. 7.) 



St. Bieneanum forma spetsbergensis Nordst. Desm. Arctose, 1875, p. 32, 

 t. 8, f. 35 ; Boldt, Siber. Chloropliy. 1885, p. 110 ; Roy & Biss. Scott. 

 Desm. 1893, p. 178 (sep. p. 17) ; Borg. Ferskv. alg. Ostgronl. 1894, 

 p. 25 ; Freshw. Alg. Fgeroes, 1901, p. 232 ; Larsen, Freshw. Alg. E. 

 Greenland, 1904, p. 96 ; Ferskvandsalg. Vest-Gronl. 1907, p. 348. 



Cells proportionately a little longer, not quite so 

 deeply constricted ; vertical view of triangular form 

 with straight or sometimes slightly convex- sides, or of 

 tetragonal form with slightly concave sides. Cell-wall 

 punctate as in the typical form. 



Length oo-42/i; breadth 24-38 /x ; breadth of 

 isthmus 10-14/x. 



SCOTLAND.- -Xear the summit of Lochnagar, Aber- 

 deen (Roy $ Bisxett). 



Geogr. Distribution.- -Faeroes. Spitsbergen. Green- 

 land. Siberia. 



Var. ellipticum Wille. (PI. CXX, fig. 8.) 



St. Bieneanum var. ellipticum Wille, Ferskv. Alg. Nov. Semlj. 1879, p. 50, 

 t. 13, f. 49; Boldt, Siber. Chlorophy. 18S5, p. Ill; West, Alg. W. 

 Ireland, 1892, p. 177 ; Schmidle, Beitr. Algeiin. ScliAvarzwald. u. 

 Kheineb. 1893, p. 109, t, 5, f . 29 ; W. & G. S. West, Alg. S. England, 

 1897, p. 494 ; Schmidle, Lappmark Susswasseralgen, 1898, p. 58 ; 

 Liitkem. Desni. Millstattersees, 1900, p. 19 ; Larsen, Ferskvandsalg. 

 Vest-Gronl. 1907, p. 348. 



Semicells rather narrowly elliptic, angles rounded ; 

 cell- wall punctate, with the punct illations arranged in 

 concentric series around the angles. 



