156 BRITISH DESMID1ACEJ1. 



Ralfs' figs. 5 a-g represent another form of the species 

 which we have here named " var. Ralfsii." This is the 

 form which most authors, ourselves included, have until 

 recently regarded as the type form of the species, an error 

 due to the fact first pointed out by Nordstedt in 1903, that 

 no one had taken the trouble to go back to Half's' original 

 account in the ' Annals and Magazine of Natural History ' 

 for 1845. 



St. Farquliarsonii Roy & Biss. is this species in its most 

 typical form. 



Var. hibernicum nol. (PI. CXXIV, figs. 5-9.) 



St. orbicidare forma in Wittr. & Nordst. Alg. Exsic. 1878, no. 167. 



? St. cordatum Gay, Monogr. loc. Conj. Montpellier, 1884, p. 65, t. 2, f . 7 ; 



De Toni, Syll. Alg. 1889, p. 1194. 

 St. hibernicum West, Alg. W. Ireland, 1892, p. 177, t. 23, f. 6 ; Alg. Engl. 



Lake District, 1892, p. 731 ; Notes Alg. II, 1900, p. 296, t. 412, f. 20. 

 St. orbiculare var. extensum Nordst. forma major Schmidle, Beitr. alp. Alg. 



1896, p. 61. 



St. orbiculare in Nordst., Wittr., & Lagerh. Alg. Exsic. 1903, no. 1472 ; 

 i'asc. 35, 1903, p. 9 [in part], f. 1-6 (p. 10). 



Cells often a little larger than the type ; semicells 

 with the basal angles less rounded and the apex broadly 

 truncate ; vertical view somewhat variable in the 

 width of the angles ; cell-wall punctate as in the 

 type. 



Length 42-65 p. ; breadth 36-56 /x; breadth of 

 isthmus 9*5-20 p.. 



ENGLAND. Near Bowness and Loughrigg, "West- 

 moreland ! 



IRELAND.- -Near "Westport, Mayo ! 



Geogr. Distribution.- -France (?). Austria. Sweden. 



This is the largest form of St. orbiculare and is principally 

 charHcterized by the more pronounced basal angles of the 

 semicells and the flattened apices. 



Var. Ralfsii var. noo. (PI. CXXIV, figs. 12, 13, 15, 16.) 



St. orbiculare Ealfs, Brit. Desm. 1848, t. 21. f. 5 a-g ["not 5 h and i] ; Delp. 

 Desm. subalp. 1877, p. 37 (sep. p. 133), t. 10, f. 8-10; Wille, Ferskv. Alg. 

 Nov. Semlj. 1879, p. 49 ; Gay, Monogr. loc. Conj. Montpellier, 1884, 

 p. 65 ; Cooke, Brit. Desm. 1887, t. 51, f. 7 [figures poor] ; Hansg. Prodr. 

 Algenfl. Bohm. 1888, p. 254; West, Alg. N. Wales, 1890, p. 293; Alg. 

 W. Ireland, 1892, p. 176; Alg. Engl. Lake Distr. 1892, p. 731 ; Roy '& 

 Biss. Scott. Desm. 1893, p. 23 (sep.) ; W. & G. S. West, Alg. S. Engl. 



1897, p. 494 ; Alga-fl. Yorks. 1900, p. 100 ; Alg. N. Ireland, 1902, p. 49 ; 



