STAURASTRUM. 31 



land ! Haves Water, Red Tarn, Grasmere and Winder- 



9J 



mere, Westmoreland ! 



WALES.- -In the plankton ! 



SCOTLAND.- -X. of Stornoway, Lewis ! General in the 

 plankton of many lochs in the mainland and Outer 

 Hebrides ! Plankton of Shetlands ! 



IRELAND.- -Plankton of Gahvay and Kerry ! 



Geocjr. Distribution.- -Norway. Finmark. Finland. 

 Eussian Lapland. X.W. Canada. 



This variety is very frequent in plankton, and sometimes 

 occurs in abundance. It is distinguished from typical St. lunatum 

 by its more angular semicells, in which the angles are more pro- 

 duced, and end in much smaller spines. There is no very obvious* 

 constriction at the base of the spines. The entire cell is finely 

 granulated, the granules being very acute and arranged in con- 

 centric series round the angles. It is similar to St. lit t/ turn L 

 alpestris Schmidle (in ' (Est. Bot. Zeitschr.' 1895, p. 24, t. 16, 

 f . 27), but differs in the more attenuated angles of the semicells 

 which run directly into the spines, whilst its granulation is also 

 more uniform. 



CO. Staurastrum cornutum Arch. 

 (PL CXXXIII, fig. 16.) 



Staurastrum cornutum Arch, in Ann. Mag. Nat. Hist. 1881, p. 232 ; Cooke r 

 Brit, Desm. 1887, p. 190 ; De Toni, Syll. Alg. 1889, p. 1175 ; Roy & Biss. 

 Scott, Desm. 1893, p. 180, t, 3, f. 5; Gronblad, Desm. Keuru, 1920, p. 60, 

 t. 2, f. 27, 28, t, 3, f. 54, 55. 



Small ; length and breadth equal ; semicells oval, 

 diverging widely from the isthmus, which is broad ; 

 sides with one simple or deeply cleft stout spine ; end 

 with about six small emarginate spines, and two rows 

 of similar spines within the margin ; end view triangular, 

 with a stout spine at each angle, and about four small 

 emarginate spines on the margin of the straight sides, 

 and one row of similar spines within the margin (Roy}. 



Zygospore unknown. 



Length and breadth, without side spines, 27 p ; 

 isthmus 1 1 [JL ; length of spine 9 y. . 



