170 BRITISH DESMIPIACE/fc. 



more rounded angles and straighter sides of the vertical 

 view. It can also be compared with St. punctulatum var. 

 muricatiforme Sclimidle ( = St. mnricatiforme Schmidle, 'Beitr. 

 alp. Alg./ 1896, p. 162, t. 16, f. 14, 15), from which it is 

 distinguished by its smaller size, its deeper constriction and 

 much narrower sinus, its more compressed and flattened 

 semicells, and by the rounder angles and straighter sides of 

 the vertical view. 



31. Staurastrum alternans Breb. 

 (PI. CXXVI, figs. 8, 9.) 



Staurastrum income Ralfs. in Ann. Mag. Nat. Hist. 1845., p. 155, t. 11, 

 f. 2 [not St. tricorne (Breb.) Menegh.l. 



St. alternans Breb. in Kalis' Brit, Desm. 1848, p. 132, t. 21, f. 7 ; Arch, 

 in Priteli. Infus. 1861, p. 741, t. 2, f. 16, 17 ; Delp. Desm. subalp. 1877, 

 p. 47, t. 11, f. 39-42; Wille, Ferskv. Alg. Nov. Semlj. 1879, p. 53; 

 :- Wolle, Desm. U. S. 188i, p. 128, t. 41, f. 26-28 ; Cooke, Brit. Desm. 

 1887, p. 162, t. 54, f. 7 "figures very poorj ; Hansg. Prodr. Algenfl. 

 Bohm. 1888, p. 254; Boldt, Desm. Gronland, 1888, p. 37; DeToni, Syll. 

 Alg. 1889, p. 1193 ; West, Alg. N. Wales, 1890, p. 294; Alg. W. Ireland, 

 1892, p. 180; Alg. Engl. Lake Distr. 1892, p. 732; Liitkem. Desm. 

 Attersees, 1893, p. 567 ; Roy & Biss. Scott. Desm. 1893, p. 16 (sep.) ; 

 y Turn. Freshw. Alg. E. India, 1893, p. 105, t. 16, f. 6 ; Nordst. Index 

 Desm. 189(5, p. 41 ; W. & G. S. West, Alg. S. England, 1897, p. 494 ; 

 Sclimidle, Lappmark Siisswasseralgen, 1898, p. 58: W. & G. S. West, 

 Alga-fl. Yorks. 1901, p. 101; Borg. Alg. Faroes, 1901, p. 230; W. & 

 G. S. West, Alg. N. Ireland, 1902, p. 51 ; Him, Desm. Finland, 1903, 

 p. lv ; Larseii, Freshw. Alg. E. Greenland, 1904, p. 95; W. & G. S. 

 West, Freshw. Alg. Orkneys and Shetlands, 1905, p. 25; Borge, 

 Beitrage Alg. Schwedeii, 1906, p. 46 ; G. S. West, Alg. Third Tan- 

 ganyika Expedit. 1907, p. 125 ; Alg. Tan Yean, 1909, p. 28 ; W. & 

 G. S. West, Brit. Freshw. Phytoplankton, etc., 1909, p. 181. 



Phy cast nun trilobatum Kivtz. Spec. Alg. 1849, p. 179. 



P. Ralfsii Nag. Gatt. einzell. Alg. 1849, p. 125. 



Didymidium (Staurastrum) punctulatum A minus y alternans Keinsch, 

 Algenfl. Frank. 1867, p. 160. 



St, dilatatum b. alternans Eabenh. Flor. Europ. Alg. Ill, 1868, p. 207. 



Cells small, as long as broad, twisted at the isthmus 

 through 60, deeply constricted, sinus open and 

 acute-angled ; semicells rather narrowly oblong- 

 elliptic, lateral angles rounded, apex flattened in the 

 middle (but convex if the cell is very slightly oblique). 

 Vertical view triangular, angles of one semicell alter- 



O ~ 



nating with those of the other, sides concave, angles 

 rounded. Cell-wall finely granulate, granules arranged 

 in concentric rings around the angles, but scattered 

 and somewhat reduced in the middle of the apex. 



