STAURASTEUM. 41 



SCOTLAND. General ! Zygospores from Heughhead, 

 Kincardine (Roy & Biss.). Rare in the plankton ! 

 IRELAND. Donegal ! Clare Island. Mavo ! Galwav ! 



c? t */ 



Kerry ! Dublin and Wicklow (Arch.). Armagh ! Lon- 

 donderry ! Plankton of L. Xeagh ! 



Geoyr. Distribution.- -France. Germany. Switzerland. 

 Galicia in Austria. Hungary. Servia. Italy. Norway. 



f V W 



Finmark. Sweden. Finland. Faeroes. Greenland. 

 Japan. United States and Alaska. Brazil. 



St. Avicula is widely distributed, though rarely occurring in 

 abundance. Its uniform granulation and the pair of minute 

 spicules at each angle of the broadly ovate semicells distinguish 

 it. Occasionally one or more of the granules near the angles 



/ O 



tend to develop also into short spines. 



Var. subarcuatum (Wolle)West. (Pl.CXXXIILng.il.) 



rum ji(/]>illn*ti)n Kirchn. Alg. .Schles. 1878, p. 17<>. 

 St. denticiilntuin Elf. Anteck. Finska Desm. 1881. p. 9. t. 1. t. .~>. 

 St. subarcuatum Wulle, Desm. U. S. 1884. p. 140. t. 415. t. 1/i, Hi : De Toni, 



Syll. Alg. 1889, p. 11 (id. 



St. Avicula var. verrucosum West, Alg. W. Irelajul. 181)2, p. 174. t. 23, t'. 2. 

 St. Avicula var. subarcuatiun \\V>t & ('<. S. \\Vst, Xe\v Brit. Freslnv. Alu. 



1894, p. 10 ; Alg. 8. England, 1897, p. 493 ; Alga-n. V.rks. 1902. p. 98 ; 



Alg. X. Ireland, 1902, p.~4l> : Freshw. Alir. nrkney.s and Shet lands, 190.'i, 



p. 24: Brit. Freshw. Phytoplankton, 1909. ]>. 17>>. 



Semicells more distinctly triangular than in the type, 

 dorsal margin nearly straight, sinus more open and acute, 

 angles of cell very slightly produced, membrane dis- 

 tinctly granulate, granules arranged in concentric rows 

 round the angles. 



Length 22*5-27 k u ; breadth, including spines, 30-37 JJL ; 

 breadth of isthmus 8 '5-10 JJL. 



ENGLAND. Mossdale Moor and Widdale Fell, W. 

 Yorks ! Stokesley, X. Yorks ! Epping Forest. Essex ! 

 New Forest, Hants ! 



WALES. In the plankton. 



SCOTLAND. --Loch Kinnelan, Ross; Tonley Pond, 

 Aberdeen (Roy d- Biss.). Plankton of Lochs na Cloiche 

 Sgoiltj Bairness, and na Cliche, Inverness! Plankton of 

 Lochs Cuthaig, Fadaghoda, Roinebhall, and Stranabhat, 



