96 BRITISH DESMIDIACE^. 



** Cells with prominent accessory spines, either simple or 

 emarginate, but of considerable length, on the " body ' 

 of the cell. 



151. St. vestitum. 



152. St. aculeatum. 



153. St. controversum . 



154. St. cosmospinosum. 



155. St. HeimerUanum. 



156. St. Sebdldi. 



157. St. oxyacanihum. 



158. St. dorsidentiferum. 



159. St. acicidiferum. 



111. Staurastrum gracile Ralfs. 

 (PI. CXLIV, figs. 3-7.) 



Staurastrum gracile Ralfs, in Ann. Mag. Nat. Hist. 1845, p. 155, t. 11, f. 3 ; 

 Brit. Desm. 1848, p. 136, t. 22, f. 12 ; Arch, in Pritch. Infus. 1861, p. 742, 

 t. 3, f. 28, 29 ; Rabenh. Krypt. Flor. Sachs. 1863, p. 192 ; De Not. 

 Desm. Ital. 1867, p. 54, t. 5, f. 49 ; Rabenh. Flor. Europ. Alg. 1868, 

 p. 211; Arch, in Quart, Journ. Micr. Sci. v. 10, 1870, p. 86; Nordst, 

 Norges Desm. 1873, p. 74 ; Jacobs. Desm. Danem. 1875, p. 207 ; 

 Delp. Spec. Desm. subalp. 1877, p. 153, t. 12, f. 12-21 ; Kirchn. Alg. 

 Schles. 1878, p. 167 ; Wolle, Desm. U. S. 1884, p. 133, t, 43, f. 16, 17 ; 

 Cooke, Brit. Desm. 1887, p. 170, t. 58, f. 6 ; De Toni, Syll. Alg. 1889, 

 p. 1209 ; Anderss. Sverig. Chloroph. 1890, p. 12 ; West, Alg. W. Ireland, 

 1892, p. 181 ; Roy & Biss. Scott. Desm. 1893, p. 20 ; West & G. S. West, 

 Alg. S. England, 1897, p. 495, t. 6, f. 27 ; Desm. U. S. 1898, p. 317, t. 18, 

 f. 7 ; Ale. X. Ireland, 1902, p. 54 ; Alga-fl. Yorks. 1902, p. 105 ; Ale. 

 Ceylon, 1902, p. 190 ; Scott, Freshw. Plankt. I, 1903, p. 549, t. 18, f. id"; 

 Freshw. Ale;. Orkneys & Shetlands, 1905, p. 27 ; Teodoresco, Mater, flor. 

 Alg. Roumania, 1907, p. 186 ; Kofoid, Plankt. Illinois, 1908, p. 61 ; 

 Gutw. Flor. Alg. Mont. Tatr. 1909, p. 475 ; Wahlburg, Bidr. kanne. 

 Littois-trask, 1913, p. 47, t. 1, f. 7. 



Phycastnun gracile Kiitz. Spec. Alg. 1849, p. 181. 



Diclyntidiion (Staurastrum) gracile Reinsch, Algenfl. Frank. 1867, p. 166. 



Cells variable, usually of small or medium size, 2-2^ 

 times longer than broad, excluding the processes; con- 

 striction slight, usually an acute notch ; semicells 

 variable in form, usually more or less cup-shaped, 

 lower angles broadly rounded, lateral margins nearly 

 vertical or slightly diverging, rarely slightly concave, 

 semicells usually broadening slightly towards the apex, 

 which is very slightly convex ; upper angles produced 

 to form long slender processes of variable length, each 

 tipped with 3 or 4 minute spines, and provided with 

 several concentric series of denticulations ; processes 



