184 BRITISH DESMIDIACEJE. 



that species. It is essentially an alpine and arctic variety, 

 and often attains a larger size tliaii the average specimens of 

 the type. 



The semicells are somewhat variable in shape, triangular 

 and quadrangular forms being almost equally common. The 

 bluntness of the angles and the rather finer granulation are 



o o 



the principal features of the variety. 



We have observed one zygospore (PI. CXXVII, fig. 13) 

 which we figured in 1900 as that of St. punctulatum (Cf. W. 

 & G. S. West, 'Notes Alg II,' t, 412, f. 13). 



Var. coronatum (Scliraidle) nob. 



St. alternans var. coronatum Schmidle, Weitr. Beitr. Algenfl. Rheineb. u. 

 Schwarzwald, 1895, p. 82, t. 1, f. 21; Schroder, Alg. Versuchsteiche 

 Schles. Fischereiv. Trachenberg, 1897, p. 42. 



Semicells with six rounded warts of small size in the 

 central part of the apex, one opposite each side and 

 each angle. 



Length 28 p. ; breadth 22 p.. 



ICELAND. Aclrill Island, Mayo ! Xear Round stone, 



/ 



Gralway ! 



Geogr. Distribution. Germany. 



This variety has the proportions and also the acutely 

 rounded and slightly inflated angles of St. punctulatum. The 

 apical warts are very distinctive. 



Var. pygmasum (Breb.) nob. (PL CXXVIII, 



figs. 1,2.) 



Staurastrum pygmseum Breb. in Ralfs' Brit. Desm. 1848, p. 213, t. 35, f. 

 26 [description and figure very poor] ; Arch, in Pritch. Int'us. 1861, p. 

 740'; Rabenh. Flor. Europ. Alg. Ill, 1808, p. 220; Wittr. Gotl. 6l. 

 sotv. Alg. 1872, p. 53, t. 4, f. 10 ; Cooke, Brit. Desm. 1887, p. 157, t. 54, 

 f. 1 [figures poor] ; Hansg-. Prodr. Algenfl. Bohm. 1888, p. 213 ; De 

 Toni, Syll. Alg. 1889, p. 1181 ; West, Alg. N. Wales, 1890, p. 293 ; Alg. 

 W. Ireland, 1892, p. 177 ; Alg. Engl. Lake Distr. 1892. p. 731 ; Liitkem. 

 Desm. Attersees, 1893, p. 565 ; Roy & Biss. Scott. Desm. 1894, p. 24 

 (sep.) ; Borg. Ferskv. Alg. Ostgrdnl. 1894, p. 26 ; Norclst. Index Desm. 

 1M>6, p. 214; W. & G. S. West, Alg. S. England, 1897, p. 494; 

 Schmidle, Lappmark SiissAvasseralgen, 1898, p. 56 ; W. & G. S. West, 

 Alga-fl. Yorks. 1901, p. 102 [in part] ; Borg. Fresh w. Alg. Faeroes, 

 1901, p. 230; W. & G. S. West, Alg. N. Ireland, 1902, p. 50; Him, 

 Desm. Finland, 1903, p. 23 ; Cushman in Rhodora, v, 1903, p. 222 ; in 

 Bull. Torr. Bot. Club, xxxii, 1905, p. 552 ; W. & G. S. West, Freshw. 

 Alg. Orkneys and Shetlands, 1905, p. 1!5 ; Borge, Beitriige Alg. 

 ScliAveden, 1906, p. 45 ; Larsen, Ferskvandsalg. Vest-Gronl. 1907, p. 

 353. 



