246 BRITISH DESMIDIACE^. 



C. pulcherrimum differs principally from its close allies, 

 C. binum and C. subspeciosum, in its deeper constriction and 

 in the broadly rounded apices of its semicells. Its central 

 tumour is considerably smaller than that of C. binum, but is 

 similar in general aspect to that of C. subspeciosum. 



210. Cosmarium binum JN T ordst. 

 (PI. LXXXVIII, figs. 10-14) 



Cosmarium binum Nordst. in Wittr. <t Nordst. Alg. Exsic. 1880, no. 383 ; 



fasc. 21, 1889, p. 39 ; De Toni, Syll. Alg. 1889, p. 993 ; Liitkem. Desm. 



Attersees, 1893, p. 559 ; Nordst. Index Desm. 1896, p. 61 ; West & G-. S. 



West, Freshw. Alg-. Ceylon, 1902, p. 171 ; Borge, Alg. erst. Regnell. 



Expedit. II. Desmid. 1903, p. 101, t, 3, f. 31 [forma] ; G-. S. West, Alg. 



Third Tang. Expedit. 1907, p. 121. 



C. binum Nordst. var. Racib. Desm. Nowe, 1889, p. 93, t. 5, f. 25. 

 C. pulcherrimum Nordst. var. truncatum Grutw. Wahr. d. Prioritat, 1890, 



p. 70 ; Flor. Glon. Okolic Lwowa, 1891, p. 58, t. 2, f. 21 ; Schmidle, Alg. 



aus Sumatra, 1895, p. 304, t. 4, f. 11. 

 Ursinella bina Kuntze, Revis. gen. plant. 1891, p. 924. 

 Cosmarium costatum as figured by Johnson, Rare Desm. U. S. II, 1895, 



p. 293, t. 240, f. 31. 



Cells of medium size or less, 1-g ^ times as long as 

 broad, deeply constricted, sinus very narrowly linear 

 with a slightly dilated extremity ; semicells pyrami- 

 date-trapeziform, basal angles rounded-subrectangular, 

 sides moderately convex and 6-10-creiiate, apex rather 

 widely truncate and 5 6-crenate, all the crenations 

 (both apical and lateral) bigranulate or more or less 

 distinctly emarginate; towards the margins granulate, 

 granules arranged in radial and concentric series, 

 outer three or four series binate, the remainder single; 

 in the centre above the isthmus with a conspicuous 

 tumour furnished with 6-8 vertical granulate ridges, 

 and under this tumour immediately adjacent to the 

 isthmus with a horizontal series of 5-8 rounded 

 granules. Side view of semicell ovate-oblong, with a 

 granulate tumour on each side near the base. Vertical 

 view elliptic-oblong, poles rounded, with a large, 

 rounded, granulate tumour at the middle on each side. 

 Chloroplasts axile, with two pyrenoids. 



Zygospore unknown. 



Lenth 41-90 ; breadth 30-59 ; breadth of 



