STAURASTRUM. 131 



terised by their very slightly concave or even straight margins 

 in the end view, and somewhat shorter and more broadly trun- 

 cate processes. West in 'Alg. N. Wales,' 1890, p. 90, f. 35, des- 

 cribed a variety subglabrum of this species, which seemed to be 

 almost destitute of granules. This variety has never been 

 observed since it was first described, and the original figure of 

 it scarcely gives a clear idea of its exact nature. Accordingly, 

 for the present, it must be considered a doubtful form. 



133. Staurastrum margaritaceum (Ehrenb.) Menegh. 



(PL CL, figs. 5-9.) 



Pentaslerias margaritaceum Ehrenb. Infus. 1838, p. 144, t. 10, f. 15. 

 Staurastrum margaritaceum Menegh. Synops. Desm. 1840, p. 227 ; Ralfs 

 in Ann. Mag. Nat. Hist. vol. 15, 1845, p. 157, t. 11, f. 7 ; Brit. Desm. 



1848, p. 134, t. 21, f. 9 ; Breb. Liste Desm. 185(5, p. 140 ; Arch, in Priteh. 

 Inf. 1861, p. 744, t. 3, f. 34, 35 ; De Xot, Desm. Ital. 1867, p. 53, t. 5, 

 f. 48 ; Rabenh. Flor. Europ. Alg. 1868, p. 206 ; Xordst. Xorges Desm. 

 1873, p. 28 ; Desm. Arctote, 1875, p. 33 ; Kirchn. Alg. Schles. 1878, 

 p. 166 ; Gay, Mono. loc. Conj. 1884, p. 68 ; Wolle, Desm. U. S. 1884, 

 p. 125, t, 41, f. 31-35 ; Cooke, Brit. Desm. 1887, p. 181, t. 64, f. 12 ; 

 Hansg. Prodr. Alg. Bohm. 1888, p. 212 ; De Toni, Syll. Alg. 1889, p. 1227 ; 

 West, Freshxv. Alg. X. Vorks. 1889, p. 6, t. 291," f. 11; Freshw. Alg. 

 N. Wales, 1890, p. 20, t. 6, f. 22 ; Alg. W. Ireland, 1892, p. 186 ; Alg. 

 Engl. Lake Distr. 1892, p. 21 ; Borge, Chlor. Xorske Finmark, 1892, 

 p. 8 ; Roy & Biss. Scott. Desm. 1893, p. 22 ; West & G. S. West, Xew and 

 Int. Alg. 1896, p. 160, t, 4, f. 36 ; Alg. S. England, 1897, p. 496 ; Liitkem. 

 Desm. Millstattersees, 1900, p. 22 ; Comere, Desm. de France, 1901, 

 p. 158, t. 11, f. 18 ; West & G. S. West, Freshw. Chloroph. Koh Chang, 

 1901, p. 95 ; Alga-fl. Yorks. 1902, p. 108 ; Borge, Sao Paulo Alg. 1918, 

 p. 50. 



Phycastrum margaritaceum Kiitz. Plvyc. Germ. 1845, p. 138; Spec. Alg. 



1849, p. 181. 



Ph. (Stenactinium) margaritaceum Xag. Gatt. einz. Alg. 1849, p. 128. 

 Didymidium (Staurastrum) margaritaceum Reinsch, Alg. Frank. 1867, 



p. 162 (in part). 

 Staurastrum angidosum Schmidt, Grimdl. Algenfl. Liineb. Heide, 1903, 



p. 18, t. 1, f. 3. 



Cells small, about as long as broad, or often slightly 

 longer, constriction not deep, sinus open ; semicells 

 variable in form, cup-shaped, subspherical or subfusi- 

 form, upper angles of the cell produced to form short 

 obtuse processes, projecting horizontally, or sometimes 

 slightly inflexed ; cell-wall rough with minute granules, 

 arranged in concentric series round the angles, some- 

 times with a distinct circle of granules round the base 

 of the semicell. Vertical view 3-9-angled, more often 



