264 BRITISH DESMIDIACEJ;. 



ENGLAND.- -Trougli at Ambleside, Westmoreland ! 

 Near Settle, Penyghent, and Cautley Spout, "W. 

 Yorks ! 



Geogr. Distribution. - Galicia in Austria. Nova 

 Zembla. 



This species should be very carefully contrasted with 

 C. notabile Breb. and C. Nagelianum Breb., especially the 

 former, from which it differs only in the granulation of the 

 cell-wall and in the presence of two pyrenoids in each 

 semicell. 



220. Cosmarium tumens Nordst. 

 (PI. XC, figs. 19, 20.) 



Cosmarium tumens Nordst. Desm. Spetsb. 1872, p. 36, t. 7, f. 23 ; Nordst. 



Index Desm. 1896, p. 262 ; West & G. S. West, Alga-fl. Yorks. 1900, 



p. 85. 

 Dysphinctium tumens (Nordst.) Hansg'. Prodr. Algenfl. Bohm. 1888, p. 278; 



De Toni, Syll. Alg\ 1889, p. 892 ; Gutw. Alg\ prsecip. Diatom., Asia 



central, atque in China collect. 1903, p. 205, t. 9, f. 4. 



Cells rather under medium size, about 1J times as 

 long as broad, moderately constricted, sinus open and 

 acute-angled ; semicells broadly subcircular-ovate, gra- 

 dually narrowed from a broad, convex base to a rather 

 narrow, subtruncate apex, sides convex, entire margin 

 crenulate-granulate or undulate-crenulate, crenulations 

 about 16 of which 4 are apical; towards the margin 

 with several more or less irregular series of granules 



o o 



(sometimes with an indistinct radial disposition), and 

 across the base immediately above the isthmus with 

 3-4 somewhat indistinct transverse series of granules, 

 with a smooth area in the centre of the semicell. Side 

 view of semicell ovate from a broad base, sides straight 

 or very slightly concave, apex broadly rounded. Ver- 

 tical view broadly elliptic, poles very bluntly pointed, 

 margin crenulate, granules disposed approximately in 

 transverse series. Chloroplasts axile, with one large 

 central pyrenoid. 



Zygospore unknown. 



Length 48-51 ^ ; breadth 30-35 ^ ; breadth of isth- 

 mus 17-24 * thickness 27-30 *. 



