100 BRITISH DESMIDIACE^:. 



described specimens from Madagascar in that the sides of the 

 semicells are simple, without denticulations or undulations, and 

 the apical teeth of the processes are considerably larger. 



Var. coronulatum Boldt. (PL CXLIV, fig. 10.) 



St. gracile v&r. coronulatum~B6ldt, Sibir. Chlorophy. 1885, p. 116, t. 5, f. 28 j 

 De Toni, Syll. Alg. 1889, p. 1209 ; West, Alg. Engl. Lake Distr. 1892, 

 p. 20, t. 9, f. 36 ; Liitkem. Desm. Attersees, 1893, p. 567. 



Cells sometimes rather smaller than in the type, often 

 more depressed and with slightly shorter processes ; 

 apex of semicell slightly convex, with two emarginate 

 processes at the top of each face ; vertical view triangular 

 or quadrangular, with two emarginate verrucse within 

 each lateral margin. 



Length 21-36 fj. ; breadth, including processes, 32 '5- 

 43 [j. ; breadth of isthmus 6-11 [i. 



ENGLAND. Bowness, Westmoreland ! 



Geogr. Distribution. Germany. Austria. Siberia. 



Var. tenuissima Boldt. (PL CXLIV, fig. 11.) 



St. gracile var. tenuissima Boldt, Sibir. Chlorophy. 1885, t. 5, f. 29 (without 

 description) ; Roy & Biss. Scott. Desm. 1893, p. 20. 



Cells more depressed than in the type ; semicells 

 subfusiform, produced at the lateral angles to form 

 processes longer and more slender than usual. Vertical 

 view quadrangular, with 3 tiny granules within each 



concave margin. 



Length 18 [i ; breadth, excluding processes, about 14 p.; 

 with processes, 40 y. ; breadth of isthmus 6 JJL. 



SCOTLAND.- -In Skye and at Brin, Inverness ; Haugh- 

 ton and in Glen Clunie, Aberdeen ; Crathes and Glen 

 Dye, Kincardine ; Glen Garry, Perth (Roy & Biss.). 



Geogr. Distribution. Siberia. 



Var. nanum Wille. (PL CXLIV, figs. 8, 9.) 



St. gracile var. nanum Wille, Norges Ferskv. Alg. 1880, p. 46, t. 2, f. 31 j 

 Racib. Nonn. Desm. Polon. 1885, p. 33, t. 12, f. 6; De Toni, Syll. Alg. 

 1889, p. 1209 ; West, Alg. W. Ireland, 1892, p. 182 ; West & G. S. West, 



