68 BRITISH DESMIDIACEJE. 



Cells minute, about as long as broad, deeply con- 

 stricted, sinus open but acute ; semicells broadly trun- 

 cate-pyramidate, sides straight (or yery faintly concave), 

 angles acute, the upper ones faintly subapiculate, apex 

 widely concaye, in the centre of the semicell with a 

 papilla. Side view of semicell subcircular, with a 

 papilla at the middle on each side. Vertical view 

 elliptic, with apiculate poles and a papilla at the middle 

 on each side, ratio of axes (without the papillae) 1 : 2. 

 Cell-wall smooth. Chloroplasts axile with a small 

 central pyrenoid. 



Zygospore unknown. 



Length 9' 5-10' 5 ^ ; breadth 9 "5-1 0*5 ^ ; breadth of 

 isthmus 2 JJL ; thickness 6 JJL. 



ENGLAND. Puttenham Common, Surrey ! 



Geoc/r. Distribution.- -Madagascar. 



This minute species should he compared with C. Sinostegos 

 Schaarschm. and its var. obtusius Gutw., from which Desmids 

 it differs in the form of its basal angles, the apiculate apical 

 angles,, and in the concave apex. 



89. Cosmarium helcangulare Nordst. 

 (PI. LXXI, fig. 7.) 



Cosmarium helcangulare Nordst. Bornh. Desm. 1888, p. 199, t. 6, f . 16-18 ; 

 De Toni, Syll. Alg. 1889, p. 960 ; G-utw. Flor. Glon. Okolic Tamapola, 

 1894, p. 87, t. 3, f . 44 ; Nordst, Index Desm. 1896, p. 138 ; West & GK S. 

 West, Alg. S. England, 1897, p. 486 [printer's error "hexangulare"^. 



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



Cells minute, a little longer than broad, deeply con- 

 stricted, sinus narrow but slightly open ; semicells 

 transversely rectangular - trapeziform, sides almost 

 straight, slightly diverging upwards, lower angles 

 rounded, upper angles produced upwards into sub- 

 mamillate processes, apex in the middle truncate or 

 slightly convex. Side view of semicell subcircular. 

 Vertical view elliptic, ratio of axes about 1:2. Cell- 

 wall smooth. 



Zygospore unknown. 



Length 11*5-14 /x; breadth H'5-12jLt; breadth of 

 isthmus 4'4-5'4 p. ; thickness 6-7'4 p. 



