46 BRITISH DESMIDIACE.E. 



semicell, 8 in the upper series (just within the apex) 

 and 5-6 iu the lower series. Side view of semicell 

 circular, with 3 prominent granules on each side. 

 Vertical view elliptic, poles somewhat conical, with 

 5-6 granules at the median part of each side and 3 

 others within them. Chloroplasts axile, with two 

 pyrenoicls in each semicell. 



Zygospore unknown. 



Length 36-50 //, ; breadth 32*5-45 p. ; breadth of 

 isthmus 9-14 ju, ; thickness 19-24/x. 



SCOTLAND.- -Rhiconich, Sutherland ! 



Geoyr. Distribution.- -Bohemia in Austria. Hungary. 

 Xorway. Sweden. Poland. N. Russia. Siberia (var.) 

 China. Japan (var.). India. Ceylon (var.). Java. 

 Madagascar (and vars.). Abyssinia. Central Africa 

 (var.). United States (and vars.). 



C. taxichondrum is a very rare British species, and is only 

 known to occur in these islands iu its typical form. In tropical 

 and subtropical countries it is, however, much more abundant, 

 and exhibits considerable variation. There are about fourteen 

 named varieties, some of which are very characteristic and 

 retain fairly constant characters. 



251. Cosmarium prominulum Racib. 

 (PL GUI, fig. 2.) 



Cosmarium prominulum Eacib. Nonn. Desm. Polon. 1885, p. 79, t. 11, f. 7 ; 



De Toni, Syll. Alg. 1889, p. 1004 ; West, Alg. W. Ireland, 1892, p. 149 ; 



Ltitkem. Desm. Attersees, 1893, p. 550 ; Key & Biss. Scott. Desm. 



1894, p. 172 ; Nordst. Index Desmid. 1896, p. 206. 

 Ursinella prominula Kuntze, Eevis. gen. plant. 1891, p. 925. 



Cells very small, as long as broad, deeply constricted, 

 sinus open with a rounded extremity ; sernicells sub- 

 hexagonal, twice as wide as their height, lateral angles 



o * o J o 



obtusely mamillate, apex widely truncate, within each 

 lateral angle with a very small protuberance. Side 

 view of semicell rhomboid, lateral angles and apex 

 rounded, upper sides concave. Vertical view rhom- 

 boid-elliptic, with a large tumour at the middle on 

 each side, and a very small one on each side close to 



