14 BRITISH DESMIDIACE.E. 



Geogr. Distribution.- -Fiance. Austria. Servia. Nor- 

 way. Sweden. United States. Colombia. 



In the sterile condition this species can scarcely be distinguished 

 from the one following, namely, St. pterosporum Lund. When 

 zygospores are present the two cannot be confused, since the 

 zygospores of St. O'Mearii are spherical and spiny, whilst in 

 St. pterosporum they are smooth and angular. The sterile cells 

 of St. Mearii are somewhat larger than those of St. ptero- 

 sporum, whilst the spines are also considerably longer and stouter. 

 It is also very similar to some forms of St. dejectum, but is usually 

 smaller and less deeply constricted. 



Var. minutum West. (PL CXXXII, fig. 9.) : 



Staurastrum 0" Mearii var. minutum West, Alg. W. Ireland, 1892, p. 172, 

 t. 22, f. 15. 



Cells minute, smaller than in the typical form, a 

 little shorter than broad, excluding the spines, apex of 

 semicells slightly concave, spines proportionately longer ; 

 angles in vertical view extremely acute. 



Length, without spines, 7-8 pi ; breadth, without 

 spines, 10 [i ; length of spines lOjz ; breadth of isthmus 



5 {/,. 



SCOTLAND. Lewis, Outer Hebrides ! 

 IRELAND. Cromagloun, Co. Kerry ! 



48. Staurastrum pterosporum Lund. 

 (PL CXXXII, figs. 1-4.) 



Staurastrum pterosporum Lund. Desm. Suec. 1871, p. 60, t. 3, f. 29 ; Arch, 

 in Ann. Mag. Nat. Hist. 1881, p. 233 ; Cooke, Brit, Desm. 1887, p. 143, 

 t. 50, f. 2 ; ? Nordst. Freshw. Alg. N. Zealand, 1888, p. 40 ; De Toni, 

 Syll. Alg. 1889, p. 1143 ; Gutw. Flor. Glon. Okolic Lwowa, 1891, p. 65 ; 

 Roy & Biss. Scott. Desm. 1894, p. 24 ; ? West & G. S. West, Some N. Amer. 

 Desm. 1896, p. 256 ; Alg. N. Ireland, 1902, p. 44 ; Brit, Freshw. Phyto- 

 plankton, 1909, p. 203 ; George v. Desm. Wlasina-See, 1909, p. 203 ; 

 G. S. West, Contrib. Freshw. Alg. Columbia, 1914, p. 1045. 



Cells minute, about as long as broad, constriction 

 not very deep, sinus widely open, acute at the apex ; 

 semicells somewhat cuneate, broadening towards the 

 apex, which is broadly truncate ; sides straight or very 



