STAURASTRUM. 1 69 



SCOTLAND.- -Plankton of Lochs Fadaglioda and an 

 Sgath, Lewis, Outer Hebrides. 

 IRELAND. --Plankton of Gal way ! 

 Geogr. Distribution.- -Finland. 



Gronblad (' Desm. Keuru,' 1920, p. 76) has suggested making var. 

 productum a distinct species, including in it St. Traunsteineri 

 Hustedt ('Desm. Bacil. Tirol.' 1911, p. 340), which he considers 

 to be merely a form of West's alga. 



157. Staurastrum oxyacanthum Arch. 

 (PL CXLIII, figs. 18, 19.) 



St. oxyacanthum Arch, in Quart. Journ. Micr. Sci. 1860, p. 757, t. 7, f. 1, 2 ; 

 in Pritch. Inf. 1861, p. 742 ; Rabenh. Krypt. Flor. Sachs. 1863, p. 193 ; 

 Flor. Europ. Alg. 1868, p. 219 ; Arch, in Quart. Journ. Micr. Sci. 1872, 

 p. 89 ; Cooke, Brit. Desm. 1887, p. 175, t. 60, f. 4 ; Borg. Bornholm. Desm.- 

 fl. 1889, p. 147 ; De Toni, Syll. Alg. 1889, p. 1219 ; Heimerl, Desm. alp. 



1891, p. 607 ; West, Alg. W. Ireland, 1892, p. 184 ; Alg. Eng. Lake Distr. 



1892, p. 20 ; Roy & Biss. Scott. Desm. 1893, p. 23 : West & G. S. West, 

 Alg. S. England,' 1897, p. 496 ; Alga-fl. Yorks. 1902, p. 106 ; Hustedt, 

 Desm. Bacill. Tirol, 1911, p. 340; West & G. 8. West, Brit. Freshw. 

 Phytoplankton, 1909, p. 203. 



St. scorpioideum var. brevis Gutw. Wahr. d. Prioritat, 1890, p. 72. 



Cells small, about 1| times broader than long, includ- 

 ing the processes, deeply constricted, sinus acute, 

 approximately rectangular ; semicells short, subfusi- 

 form or subcuneate, dorsal margin slightly convex, 

 ventral margin very tumid, semicells produced at the 

 angles to form long slender processes, very slightly con- 

 verging, tipped with about 3 minute spines and with 

 3 or 4 concentric series of minute denticulations ; apex 

 of semicell armed at the origin of each process with a 

 pair of fairly long spreading spines. Vertical view 2-4- 

 (usually 3-) angled, sides straight and smooth, with a 

 pair of stout spines projecting from just within each 

 margin, angles produced to form denticulate processes. 

 Chloroplast axile, with a central pyrenoid in each semi- 

 cell, and a pair of plates projecting into each angle. 



Zygospore unknown. 



Length 26-29 \L ; breadth, including processes, 36-40^; 

 breadth of isthmus 9 '6-10^. 



ENGLAND.- -Loughrigg !, and near Bowness (Bissett), 



