180 BKIT1SH DESMIDIACE^E. 



p. 160, t. 54, f. 6 ; Hansg. Prodr. Algenfl. Bohm. 1888, pp. 212, 25 I ; 

 Holdt, Desm. Groiiland, 1888, p. 34; De Toni, Syll. Alg. 1889, p. 1190; 

 West, Alg. N. Yorks, 1889, p. 293 ; Alg. N. Wales, 1890, p. 294 ; 

 Heimerl. Desm. alpin. 1891, p. 605; West, Alg. W. Ireland, 1892, 

 p. 179 ; Alg. Engl. Lake Distr. 1892, p. 732 ; Borge, Chlorophy. Norska 

 Finmark. 1892, p. 7 ; Gutw. Flor. gloiiow Galic. 1892, p. 134 ; Liitkem 

 Desm. Attersees, 1893, p. 566 ; Roy & Biss. Scott. Desm. 1894, p. 24 

 (sep.) ; Nordst. Index Desmid. 1896, p. 213 ; Schmidle, Beitr. alp. Alg. 

 1896, p. 62 ; W. & G. S. West, Welw. Afric. Freshw. Alg. 1897, p. 181 ; 

 Alg. S. England, 1897, p. 494 ; Alga-fl. Yorks. 1901, p. 101 ; Borg. 

 Freshw. Alg. Feeroes, 1901, p. 230 ; Bohlin, Flor. Algol, d'eau douce d. 

 Agores. 1901, p. 61, t. 1, f. 20, 21 ; W. & G. S. West, Alg. N. Ireland, 

 1902, p. 50 ; Him, Desm. Finland, 1903, p. 22 ; W. & G S. West, Scott. 

 Freshw. Plankton, I. 1903, p. 529 ; Larsen, Freshw. Alg. E. Greenland, 



1904, p. 99 ; W. & G. S. West, Freshw. Alg. Orkneys and Shetlands, 



1905, p. 25 ; Borge, Beitrage Alg. SchAveden, 1906, p. 45 ; Teodoresco, 

 Mater, flor. alg. Roumaii. 1907, p. 184; Larsen, Ferskvandsalg. Vest- 

 Gronl. 1907, p. 352 ; W. & G. S. West, Freshw. Alg. Burma, 1907, p. 

 214; G. S. West, Alg. Yan Yean, 1909, p 28; W. & G. S. West, Brit. 

 Freshw. Phytoplankton, etc., 1909, p. 183 ; Phytoplankton Engl. Lake 

 Distr. 1909, p. 139; Hustedt, Desm. et Bacill. aus Tirol, 1911, p. 337. 



Didymidium (Staurastntm) punctttlatttm Reinsch, Algenfl. Frank. 1867, 



p. 159. 

 Staurastrum ptinctulatum forma contorta Schmidle, Beitr. alp. Alg. 1896, 



p. 62. 



Cells small, a little longer than broad, deeply con- 

 stricted, often twisted at the isthmus, sinus open and 

 acute-angled (about 70) ; semicells subrhomboid- 

 elliptic, dorsal and ventral margins about equally 

 convex, angles somewhat acutely rounded. Vertical 

 view triangular (rarely 4-, and very rarely 5-angular), 

 angles acutely rounded, sides slightly retuse in the 

 middle; angles of one semicell often partly or entirely 

 alternating with those of the other. Cell-wall uni- 

 formly granulate with flattened granules, which are in 

 regular series around the angles. 



Zygospore globose, furnished with rather short 

 spines which are doubly furcate at the apex, each one 

 arising from a broadly mamillate base. 



Length 26-4O5 p ; breadth 23-36'5/ui; breadth of 

 isthmus 8-16 p. ; diam. zygosp. without spines 29-38 ^, 

 with spines 42-5 8 JJL. 



ENGLAND. - - Cumberland ! Westmoreland ! Lanca- 

 shire ! W., N., and E. Yorks. (zygospores from 

 Keighley, W. Yorks) ! Leicester (Roy). Essex ! 

 Cambridge! Warwicks ! (Wills). Worcestershire! 

 Staffordshire ! Middlesex ! Surrey (zygospores from 



