230 BRITISH DESMIDIACE.E. 



WALES.- -Snowclon!, Penygwryd (Roy), Llyn-y- 

 cwm-ffynon !, and Yr Orsedd!, Carnarvonsliire. 



SCOTLAND.- -Ross, Inverness!, Banff, Aberdeen, 

 Kincardine, Forfar !, Perth! (Roy fy Bissett). Dum- 

 barton ! Cumbrse ! Orkneys ! Shetlands ! Lewis, 

 Outer Hebrides ! 



IRELAND.- -Donegal ! Muckross, Carrantuohill, and 

 Cloonee Lough, Kerry ! Down (up to 2000 ft.) ! 



Geogr. Distribution. France. Germany. Galicia 

 in Austria. Italy. Spain. Norway. Sweden. Born- 

 holm. Finland. Poland. N. Russia. Faeroes. Ice- 

 land. jSTova Zembla. Franz Joseph Land. Spitz- 

 bergen. Greenland. Siberia. Manchuria. Sumatra. 

 E. and Central Africa. United States. Ecuador. 

 Uruguay. Patagonia. 



This species lias in the past been much confused with other 

 more or less closely allied Desmids, and it has most probably 

 a wider distribution than is indicated by its recorded localities. 

 It is distinguished from C. crenatum Ralfs by its propor- 

 tionately wider and less rectangular semicells, by its larger 

 number of crenations, and by the more evident granulation, 

 especially of the central tumour. It should also be com- 

 pared with C. suljcostatum var. Becltii, from which it differs 

 in the form of its semicells, its more rounded crenatioiis, 

 and in the nature of the granulation of its central tumour. 



Nordstedt has described and figured a trigonal variety 

 (var. triquetrum Nordst.) from Spitzbergen. 



We give a figure of a reduced form in which the granula- 

 tion of the central tumour was largely wanting (PL LXX'XVI, 

 fig. 15). 



Zygospores of C. snbcrenatum were observed by L. N. 

 Johnson from Arlington, Massachussets, U. S. A. 



Var. divaricatum Wille. (PI. LXXXVI, figs. 16-18.) 



C. subcrenatum Haiitzsch var. divaricatum Wille, Ferskv. Alg. Nov. Semlj. 

 1879, p. 40, t. 12, f. 27; Boldt, Desm. Grbnland, 1888, p. 19; Gutw. 

 Flor. Glon. Okolic Lwowa, 1891, p. 58 ; West, Alg. W. Ireland, 1892, 

 p. 150; Schmidle, Ost-Afrika Desm. 1898, p. 28. 



Semicells with the lateral crenations (except the 

 lowest smaller ones) and those at the apical angles 

 biclenticulate or truncate-emarginate, central tumour 

 furnished with 6-8 vertical series of granules. 



