118 BRITISH DESMIDIACE.E. 



Hungary. Italy. Norway. Sweden. Denmark. 

 Lapland in Russia. Faeroes. India. Singapore (var.). 

 East Africa. United States. 



This is one of the most striking species of the genus, and 

 is generally distributed over the boggy districts of the British 

 Islands. It has in the past received a number of different 

 names, largely owing to its variability and to its periodical 

 increase in size after division. The forms which have' been 

 named " var. Baillyanum" are only young individuals before 

 the development of the median girdle, which is a cylindrical 

 piece of cell-wall interpolated between the two semicells. 

 This growth subsequent to cell-division has given rise to 

 many misconceptions with regard to this species. 



The apices are usually thickened and of a darker brown 

 than the rest of the cell-wall. Some observers have remarked 

 the presence of fine striolations, but they must be of very 

 rare occurrence. We have examined thousands of specimens 

 of this species from all over the world and have never yet 

 detected them. 



Var. asperulatum var. noc. (PL XII, figs. G, 7.) 



More slender than the typical form, being 12-14 

 times longer than the diameter, rather more attenu- 

 ate, apices slightly recurved and not thickened ; cell- 

 wall colourless, minutely asperulate, being covered 

 with somewhat irregular and depressed granules. 



Length 405-418 ^; breadth 28-34^." 



ENGLAND. New Jorest, Hants ! 



6. Closterium macilentum Brcb. 

 (PI. XII, figs. 8-10.) 



Closterium macilentum Breb. Liste Desm. 1856, p. 153, t. 2, f. 36 ; Arch, 

 in Pritch. Infus. 1861, p. 747; Eabenh. Flor. Europ. Algar. Ill, 1S6.S, 

 p. 131 ; Delp. Desm. subalp. 1877, p. 107, t. 17, f. 60-62 ; Kirelm. Al\ 

 Schles. 1878, p. 137; Wolle, Desm. U.S. 1884, p. 38, t. 6, f. (i ; Hans-. 

 Prodr. Algcnfl. Bohm. 1888, p. 178 ; West, Alg. N. Wales, 1S!K), p. 284; 

 Giitw. Flor. glonow Galic. 1892, p. 120 ; Roy & Biss. Scott. Desm. 1894, 

 p. 246 ; Nordst. Index Desm. 1896, p. 162 ; West & G. S. West, Some 

 Desni. U.S. 1898, p. 283 ; Notes Alg. Ill, 1903, p. 9 (sep.). 



Arthrodia macilenta Kuntze, Kevis. gen. plant. 1891, p. 883. 



Cells of medium size, very elongate and narrow, 



