138 BRITISH DESMIDIACEJS. 



Length 25 [i ; breadth 27 pi ; breadth of isthmus 7 [.i . 

 ENGLAND. Strensall Common, N. E. Yorks. (Turn.). 



138. Staura strum hexacerum (Ehr.) Wittr. 

 (PL CXLIL figs. 11-14.) 



(?) Desmidium hexaceros Ehr. Org. Id. Raumes, 1834, p. 293 ; Inf. 1838, 

 p. 141, t. 10, f. 10. 



Binatella tricornis Breb. Alg. Falaise, 1835, p. 57, t. 8. 



Staurastrum tricorne Menegh. Synops. Desm. 1840, p. 225 ; Ralfs, Brit. 

 Desm. 1848, p. 134, t. 22, f. 11, t. 34, f . 8 a ; Arch, in Pritch. Infus. 1861, 

 p. 742 ; Nordst. Desm. Spetsb. 1872, p. 38 ; Delp. Spec. Desm. subalp. 

 1877, p. 145, t. 11, f. 48-50; Kirchn. Alg. Schles. 1878, p. 165; Wolle, 

 Desm. U. S. 1884, p. 126, t. 41, f. 36-38 ; Cooke, Brit. Desm. 1887, p. 167, 

 t. 58, f. 2 ; Nordst, Fresh w. Alg. N. Zealand, 1888, p. 41, West, Alg. 

 N. Wales, 1890, p. 18 ; Alg. Engl. Lake Distr. 1892, p. 20 ; Bohlin, 

 Flor. Alg. d'eau douce d'Agores, 1901, p. 59, f. 19. 



Phycastrum tricorne Kiitz. Phyc. Germ. 1845, p. 137. 



Ph. hexaceros Kiitz. Spec. Alg. 1849, p. 180. 



Ph. (P achy actinium} tricorne Nag. Gatt. einz. Alg. 1849, p. 126. 



Staurastrum hexacerum Wittr. Gotl. Ol. sotv. Ala;. 1872, p. 51 ; De Toni, 

 Syll. Alg. 1889, p. 1206 ; Turn. Freshw. Alg. E. India, 1893, p. 125 ; 

 Roy & Biss. Scott, Desm. 1893, p. 21 ; West & G. S. West, Alg. Mada- 

 gascar, 1895, p. 75 ; Welw. Afric. Freshw. Alg. 1897, p. 50 ; Alg. S. 

 England, 1897, p. 495 ; G. S. West, Alga-fl. Cambridge, 1899, p. 25 ; W. 

 & G. S. West, Alg. N. Ireland, 1902, p. 52 ; Alga-fl. Yorks. 1902, p. 52 ; 

 Freshw. Alg. Orkneys & Shetlands, 1905, p. 26 ; Freshw. Alg. Burma, 

 1907, p. 218. 



Cells small, about ly times broader than long, deeply 

 constricted, sinus open and acute ; semicells fusiform or 

 subtriangular, both dorsal and ventral margins convex, 

 tapering towards the angles to form very short processes 

 which end in about 3 minute teeth ; cell- wall rough 

 with tiny granules, arranged in concentric series round 

 the angles, granules in the centre of the faces and on the 

 apex of the semicell much reduced. Vertical view usually 

 triangular, lateral margins concave, angles very slightly 

 turgid. Chloroplast axile, with a central pyrenoid in 

 each semicell. 



Zygospore spherical, armed with numerous long and 

 stout conical spines, very broad at the base and bifid at 

 the apex. 



Length 23-28 \L ; breadth, including processes, 27- 

 34 \L ; breadth of isthmus 7-8 \L ; diam. zygosp., without 

 spines, 30(jt ; length of spines, about 16[ju 



ENGLAND. Cumberland ! Westmoreland, and in the 



