152 BRITISH DESMIDIACE^E. 



5-undulate. Vertical view elliptic, ratio of axes about 

 1 : 1'5, with a broad tumour at the middle on each side, 

 poles 5-undulate. Cell-wall very delicately punctate, 

 and often furnished with a few minute scrobiculations 

 more or less regularly disposed near the margin of the 

 semicells. Chloroplasts axile, each with two pyrenoids. 



Zygospore unknown. 



Length 45-60 ^u ; breadth 32-39 ^ ; breadth of 

 isthmus 15-16 /u ; thickness 23-27 /u. 



ENGLAND. Angle Tarn, Cumberland ! Blea Tarn, 

 Westmoreland ! Pilmoor, N. Yorks ! 



WALES.- -Llyn Idwal, Llyn-y-cwm-ffynon, and Capel 

 Curig, Carnarvonshire ! 



SCOTLAND. Xear Strathpeffer, Ross; Brin, Inver- 

 ness ; Upper Powlair and Slewdrum, Aberdeen ; near 

 Kingshouse, Argyll (Roy fy Bissett). Rliiconich, 

 Sutherland ! 



IRELAND.- -Near Foxford, Mayo ! Ballynahinch, 

 Lough Athry, Clifden, and near Ougliterard, Gralway ! 

 Adrigole and Castletown, Kerry ! 



Geogr. Distribution. Norway. Greenland. 



This species differs from C. undulatum in its proportionately 

 longer cells, in the semi-elliptic shape of the semicells, and in 

 the presence of the large protuberance in the centre of the 

 semicells. There are usually a few minute scrobiculations 

 near the margin of the semicells, more or less regularly 

 arranged, but rather variable in different individuals and 

 somewhat difficult of observation. 



14. Cosmarium Cucumis (Corda) Ealfs. 

 (PL LIX, figs. 18-20.) 



? ? Cosmarium Cucumis Corda in Aim. de Carlsbad, 1835, p. 206, t. 2, f . 27. 

 Cosmarium Cucumis Ealfs' Brit. Desm. 1848, p. 93., t. 15, f. 2 ; Arch, in 



Pritch. Iiifus. 1861 ; Rabenh. Flor. Europ. Alg. 1868, III, p. 161 ; 



Xordst. Desm. Spetsb. 1872, p. 36 ; Kirchn. Alg. Schles. 1878, p . 146 ; 



Wolle, Desm. U.S. 1884, p. 58, t. 15, f. 6-9 ; Nordst. Desm. Gronland, 



1885, p. 9 [forma major] ; Cooke, Brit. Desm. 1886, p. 84, t. 36, f. 11 ; 



Nordst. Bornh. Desm. 1888, p. 202 ; West, Alg. N. Wales, 1890, p. 288 ; 



Alg. W. Ireland, 1892, p. 163; Alg. Eng. Lake Distr. 1892, p. 729; Roy 



& Biss. Scott. Desm. 1894, p. 44 ; Nordst. Index Desm. 1896, p. 91 ; 



West & G. S. West, Alg. S. England, 1897, p. 485 ; Alga-fl. Yorks. 1900, 



p. 69 ; Alg. N. Ireland, 1902, p. 33. 



