STAURASTRUM. 147 



SCOTLAND.- -Plankton of Loch Langabhat, Lewis, 

 Outer Hebrides ! 



142. Staurastrum sexcostatum Breb. 

 (PL CL, fig. 14.) 



Staurastrum sexcostatum Breb. in Menegh. Synops. Desm. 1840, p. 228 ; 

 Ralfs, Brit, Desm. 1848, p. 129, t. 23, f. 5; Arch, in Pritch. Infus. 1861, 

 p. 744 ; Rabenh. Flor. Europ. Alg. 1868, p. 216 ; Xordst. Desm. Arctose, 

 1875, p. 36 ; Kirchn. Alg. Schles. 1878, p. 165 ; Racib. Xoim. Desm. Polon. 

 1885, p. 29 ; Cooke, Brit. Desm. 1887, p. 180, t. 64, f. 1 ; De Toni, Syll. 

 Alg. 1889, p. 1232 ; West, Alg. X. Wales, 1890, p. 20 ; Alg. Engl. Lake 

 Distr. 1892, p. 21 ; Roy & Biss. Scott. Desm. 1893, p. 25 ; Borge, Siissw. 

 C'hlor. Archang. 1894, p. 39 ; West & G. S. West, Alg. S. England, 1897, 

 p. 496 ; G. S. West, Variation Desm. 1899, p. 406 ; Comere, Desm. de 

 France, 1901, p. 153, t. 10, f. 16 ; Borer. Alg. Faeroes, 1901, p. 234 ; 

 West & G. S. West, Alga-fl. Yorks. 1902, p. 108. 



St. Jenneri Ralfs, in Ann. Mag. Xat. Hist. vol. 15, 1845, p. 158, t. 11, f. 8. 



Stephanoxanthium sexcostatum Kiitz. Spec. Alg. 1849, p. 184. 



Didymidium (Staurastrum) sexcostatum Reinsch, Alg. Frank. 1867, p. 166. 



Staurastrum (Pleurenterium) sexcostatum Lund. Desm. Suec. 1871, p. 74. 



Pleurenterium (Staurastrum) sexcostatum Xordst. Xorges Desm. 1873, p. 37. 



Cells of medium size, about ly-2 times longer than 

 broad, deeply constricted, sinus triangular with a minute 

 excavation at its apex ; semicells broadly elliptical, or, 

 including the processes, somewhat compressed hexa- 

 gonal in form, lateral angles very slightly produced, 

 truncate, with a circle of minute acute granules round 

 their apex ; both dorsal and ventral margins of lateral 

 angles granulate, with about 3 or 4 granules along each, 

 those near the apex of the semicell becoming emarginate ; 

 apex of semicell truncate, irregularly granulate or smooth 

 (according to the aspect) ; angles with about 2 concen- 

 tric series of denticulations ; base of semicell also with 

 a circle of prominent granules. Vertical view usually 

 hexagonal, sides concave, angles truncate, scarcely 

 produced, tipped with tiny granules, and with a second 

 series of denticulations ; lateral margins smooth, apex 

 with curved series of granules, often emarginate, extend- 

 ing from angle to angle just within the margins. 



Zygospore unknown. 



Length 40-65 JJL ; breadth, including processes, 34- 

 47 '5 pi ; breadth of isthmus 14-25 pi. 



ENGLAXD. Brother's Water, Westmoreland ! Den- 



