222 BKITISH DESMIDIACEJ-:. 



Sehmidle, Beitr. alp. Alg. 1895, p. 3S9 ; West & G. S. West, Alga-fl. 

 Yorks. 1900, p. 77 ; Alg. N. Ireland, 1902, p. 37 ; Scott. Fresliw. Plank- 

 ton, I, 1903, p. 527 ; Freshw. AL/. Orkneys and Shetlands, 1905, p. 20 ; 

 Further Contrib. Freshw. Plankton Scottish Lochs, 1905, p. 484 ; Conip. 

 Study Plankton Irish Lakes, 1906, p. 85. 

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



Cells very small, slightly longer than broad, very 

 deeply constricted, sinus narrowly linear with a very 

 slightly dilated extremity ; semicells trapeziform, 

 broader at the base than at the apex, basal angles 

 scarcely rounded, lower part of sides convex and 3- 

 undulate, upper part retuse, apical angles very slightly 

 outstanding and retuse-emarginate, apex broadly 

 truncate and 2-4-undulate, with a few small irregularly 

 scattered granules within the margins, sometimes 

 grouped in twos or threes, and with a single relatively 

 large granule in the centre. Side view of semicell 

 subcircular with a flattened granule just below the 

 middle on each side. Vertical view elliptic, with a 

 flattened granule at the middle on each side. Chloro- 

 plasts axile, with a single central pyrenoid. 



Zygospore unknown. 



Length 13'4-15*4//,; breadth 12'5-15/x; breadth of 

 isthmus 4-5 p. ; thickness 8-8' 5 p.. 



ENGLAND.- -Cumberland ! Westmoreland! W. and 

 N. Yorks! Lincolnshire! Cambridgeshire! Surrey! 

 Hants ! Devon ! Cornwall ! 



WALES. Capel Curig, Lryn-y-cwm-ffynon, Llyn 

 Idwal, and Glyder Fach, Carnarvonshire ! Dolgelly, 

 Merioneth ! 



SCOTLAND.- -Rhiconich, Sutherland ! Inverness (and 

 Skye) ! Perth ! Common in Lewis and Harris, 

 Outer Hebrides ! Orkneys ! Shetlands ! 



9> 



IRELAND.- -Donegal ! Galway ! Armagh ! Down ! 

 Lough Xeagh ! Londonderry ! Plankton of the 

 lakes of Mayo and Galway ! 



Geogr. Distribution.- -Prance. Switzerland. Ger- 

 many. Galicia in Austria. 



C. liumile is one of the most widely distributed and 

 characteristic British species of the genus. It has a most 



