96 BRITISH DESMIDIAC.EE. 



111. Cosmarium difficile Liitkem. 

 (PL LXXIII, figs. 1-3.) 



Cosmarium difficile Liitkem. Desm. Attersees, 1893, p. 551, t. 8, f . 3 : 

 Nordst, Index Desm. 1896, p. 108 ; West & G-. S. West, Alg. S. England, 

 1897, p. 487; Some Desm. U. S. 1898, p. 303; G. S. West, Alga-fl. 

 Cambr. 1899, p. 217; West & G. S. West, Alga-fl. Yorks. 1900, p. 93; 

 Alg. N. Ireland, 1902, p. 35 ; Scott. Fresliw. Plankton, I, 1903, p. 526 ; 

 Freshw. Alg. Orkneys and Shetlands, 1905, p. 22. 



Cells small, about 1^ times as long as broad, deeply 

 constricted, sinus narrowly linear with a slightly 

 dilated apex ; semicells subrectangular with an elevated 

 apex, basal angles rectangular and rounded, lower 

 part of sides slightly retuse, upper part of sides retuse 

 and converging towards the apex, which is convexly 

 truncate with a minute median depression ; with three 

 transverse rows of minute scrobiculations across the 

 sernicells, one close to the base, one above the middle, 

 and one just below the apex. Side view of semicell 

 oblong-ovate. Vertical view elliptic-oblong, with a 

 slight tumour at the middle on each side, and with a 

 ring of about 8 minute (apical) scrobiculations surround- 

 ing about 4 central ones. Cell-wall very minutely and 

 densely punctate. Chloroplasts axile, one in each 

 semicell with a central pyrenoid. 



Zygospore unknown. 



Length 28-33^; breadth 20-22'5 ^ ; breadth of 

 isthmus 4-6 /x; thickness 12'5-13/x. 



ENGLAND.- -Cumberland ! Westmoreland! AY., N., 

 and E. Yorks! Essex! Cambridge! Surrey! Hants! 

 Wilts! Devon! Cornwall! 



WALES.- -Llyn Bochlwyd, Llyn Grwynant, Y Foel 

 Fras, Grlyder Fawr, and Moel Siabod, Carnarvonshire ! 

 Merioneth ! Radnor ! 



SCOTLAND.- -Rhiconich, Sutherland! Inverness ! Ross ! 

 Forfar ! Perth ! Cumbra? ! Common in the Outer 

 Hebrides ! Orkneys ! Shetlands ! 



IRE LAND.- -Donegal ! Mayo! Gralway ! Kerry! Down 

 (up to 2000 ft.) ! Londonderry ! Antrim ! 



Geoc/r. Distribution.- -France. Germany. Austria. 

 Poland. Italy. United States. 



