258 BRITISH DESMID1ACE.E. 



truncate, sides straight and 4-crenate, crenations 

 bigranulate (except the basal one or two), apex dilated 

 and 4-crenate, apical angles (formed by the two lateral 

 of the 4 crenations) prominent and rounded, crenation 

 bigranulate (apical angles often 4-granulate) ; within 

 the margins with radiating series of granules disposed 

 in pairs within each crenation ; in the centre of the 

 semicell and towards the isthmus with a broad tumour 

 furnished with 4-7 (commonly 6) vertical granulate 

 ridges (35 granules on each ridge). Side view of 

 semicell rectangular, slightly tumid near the base at 

 each side, sides slightly retuse, apical angles rounded 

 and granulate. Vertical view elliptic, with a broad 

 crenulate tumour on each side, poles granulate. 



Zygospore unknown. 



Length 45-50 p. ; breadth 34'8-40 ju, ; breadth of 

 isthmus 18-20 p, ; thickness 23 '4-28 //,. 



ENGLAND.- Mickle Fell, N. Yorks ! 



WALES.- -Near Bethesda, Carnarvonshire ! 



SCOTLAND.- -Black Isle, Hoss ; Koynach Moor, Press- 

 whin, Craigendinnie, and Aboyne, Aberdeen ; Den of 

 Garrol and Dunis, Kincardine (Roy fy Bissrffy. Glen 

 Shee, Perth ! 



IRELAND.- -Dublin and Wicklow (Archer). 



Geor/r. Distribution.- -Norway. Russian Lapland. 

 N. Russia. Nova Zembla. Spitzbergen. Greenland. 



This alpine and arctic Desmid is exceedingly rare in the 

 British Islands. It occurs principally in boggy springs and 

 other small boggy areas high up on the mountains. It appears 

 to us to be a very distinctive species, but it should be very 

 carefully compared with C. costatum, a Desmid which occurs 

 in similar habitats. 



We figure a small form of C. hexalobum from Penyghent, 

 W. Yorkshire, which differs only in its dimensions and is 

 therefore not to be included in var. minusl&oy & Biss. ; length 

 36 f.i ; breadth 33/*; breadth of isthmus 18^. (Pl.XC, fig. 6.) 



Var. minus Roy & Biss. (PL XC, fig. 5.) 



C. hexalobum Nordst. var. minus Roy & Biss. Scott. Desm. 1894, p. 103, 

 t. 1, f. 12 ; West & G. S. West, Alg. S. England, 1897, p. 488 ; Gutw. in 

 Spraw. Kom. fizyog. Akad. Umiej. Krakow. 1898, p. 152. 



