18G BRITISH DESMIDIACE^:. 



Gronblad ( ; Desm. Keuru,' 1920, p. 90) suggests that this alga is 

 not correctly placed in St. monticulosum an opinion with which 

 the writer entirely agrees. It is perhaps nearest amongst British 

 Desmids to St. aciculiferum (West) Anders., which differs, how- 

 ever, in several respects. It seerns to have very little affinity with 

 St. monticulosum Breb. 



170. Staurastrum diplacanthum De Not. 

 (PI. CLVI, fig. 1.) 



Staurastrum diplacanthum De Not. Desm. Ital. 1867, p. 49, t. 4, f. 38 ; 



Turner, Desm. Notes, 1893, p. 345. 



St. vestitum var. diplacanthum Rabenh. Flor. Europ. Alg. 1868, p. 219. 

 St. monticulosum var. diplacanthum Nordst. in De Toni, Syll. Alg. 1889, 



p. 1157. 



Cells rather under medium size, slightly longer than 

 broad, deeply constricted, sinus open and acute ; semi- 

 cells broadly fusiform, dorsal and ventral margins almost 

 equally convex ; lateral angles very slightly produced 

 and terminating in 3 stout spines ; ventral margins with 

 a stout spine about midway" between the angles and the 

 isthmus ; dorsal margin with a pair of short distant 

 processes, bifid at their apex, and with a pair of simple 

 spines in the middle between them. Vertical view 

 triangular, sides nearly straight, angles tipped with 

 3 stout spines ; lateral margins with a pair of bifid 

 processes, and between these one or two simple spines. 

 Cell- wall irregularly punctate. 



Zygospore unknown. 



Cells about 40 \L in diameter. 



ENGLAND. Strensall Common, N. Yorks (W. B. 

 Turner}. 



Geogr. Distribution.- -Italy. 



Var. anglicum Turner. (PL CLVI, fig. 2.) 



St. diplacanthum var. anglicum W. B. Turn. Desm. Notes, 1893, p. 345, f. 10. 



Apex of semicell more convex than in the type, 

 with a ring of little verrucse ; cell- wall more spiny than 

 in the typical form. 



