232 BRITISH DESMJDIACEJE. 



on each side. Vertical view elliptic, with a prominent 

 3-crenulate tumour at the middle on each side. Chloro- 

 plasts axile, one in each semicell, with a central 

 pyrenoid. 



Zygospore unknown. 



Length 24-30 /x; breadth 22-27 /x; breadth of isth- 

 mus 6-10 jit; thickness 17-18'5/x. 



ENGLAND.- -Brothers' Water, Westmoreland ! Stren- 

 sall, XT. Yorks ! Sutton Park, War wicks ! 



WALES.- -Near Conway, and bog near Llyn Grwynant, 

 Carnarvonshire ! 



SCOTLAND. - - Skye in Inverness ! Harris, Outer 

 Hebrides ! Craig-an-Lochan, Perth ! Near Lerwick, 

 and in the plankton of Loch Brindister, Shetlands ! 



IRELAND.- -Lough Cloncarney., Donegal ! Bally na- 

 hinch and Derryclare Lough, Galway ! 



Geogr. Distribution. Germany. Gralicia in Austria. 

 Italy. Sweden. Denmark. Central Africa. 



C. subprotumidum is an uncommon British species with a 

 decided preference for the weedy margins of lakes and large 

 ponds. It stands nearest to C. protumidum JSTordst. (' Desm. 

 Spetsb/ 1872, p. 34, t. 7, f. 18), but is distinguished by its 

 somewhat different tabulation, by the reduction of the 

 marginal granules, by the different arrangement of the 

 granules as a whole, and by the less prominent central pro- 

 tuberance. It* should also be compared with C. costatum 

 Nordst. and with C. subalatum W. & Gr. S. West. 



The peripheral granules of C. subprotumidum are generally 

 very minute and not easily discernible. It is possible to 

 observe all stages between slightly retuse and minutely bi- 

 granulate marginal crenations. 



A form was observed from the West of Ireland (in small 

 pools between Clifden and Roundstone, Galway ; vide West, 

 1 Alg. W. Ireland/ 1892, p. 157, t, 24, f. 21) in which the 

 general granules were much more scattered and the central 

 granules much less distinct than usual (PI. LXXX\ 7 I, fig. 22; 

 length 32 /.t; breadth 25 /t ; breadth of isthmus 8*5 /*). 



Var. Gregorii (Roy & Biss.) W. & G. S. West. 

 (PI. LXXXYI, figs. 2:3-25.) 



C. Gregorii Roy & Biss. ined. in Gntw. AVahr. d. Prioritat, 1890, p. 69 ; 

 Gntw. Flor. Glon. Okolic Lwowa, 1891, p. 56; Flor. glonow Oalic. 



