172 BRITISH DESMIDIAUEJE. 



Length 25 /n ; breadth 22 /u ; breadth of isthmus 7 /n ; 

 thickness 13 in. 



WALES.- -Capel Curig, Carnarvonshire (Roy). 



SCOTLAND.- -Caithness, Ross, Inverness, Nairn, Aber- 

 deen, Kincardine, Forfar, Perth, Fife (Roy $- Bissett). 



This species appears to us to be very closely allied to 

 C. subcrenatum Hantzsch. There are, however., certain slight 

 differences, and as we have never observed any specimens 

 which we could with certainty refer to Roy's species, for the 

 present we keep the species separate. 



164. Cosmarium trachypleurum Lund. 

 (PI. LXXXI, figs. 2, 3.) 



Cosmarium trachypleurum Lund. Desm. Suec. 1871, p. 27, t. 2, f. 12; 



Wolle, Desm. U. S. 1884, p. 73, t. 16, f. 26-29 ; De Toni, Syll. Alg. 



1889, p. 973 ; Roy & Biss. Scott. Desm. 1894, p. 176 ; Nordst. Index 



Desm. 1896, p. 256 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 72 ; 



Notes Alg. Ill, 1903, p. 10 (sep.) ; Freshw. Alg-. Orkneys and Shetlands, 



1905, p. 19. 

 C. trachypleumm Lund. a. genuinum Kirclin. Alg. Schles. 1878, p. 151 ; 



Racib. Desm. Nowe, ] 889, p. 89. 

 Ursinella trachypleura Kuntze, Revis. gen. plant. 1891, p. 925. 



Cells rather under medium size, 1J times as long as 

 broad, deeply constricted, sinus narrowly linear with 

 a slightly dilated extremity ; semicells subreniform- 

 oblong, lateral margins each with 5-7 acute granules, 

 apex truncate (very slightly convex) and smooth, 

 within the lateral margins and below the apex with a 

 rather irregular double series of acute granules, with 

 7 large rounded granules in the centre, one central and 

 6 peripheral, and with minute punctulations between 

 them. Side view of semicell circular, sides granulate, 

 apex smooth. Vertical view elliptic, poles furnished 

 with acute granules, and with three large rounded 

 granules at the middle on each side (sometimes situated 



o \ 



on a slight tumour). Cell-wall very delicately punctate 

 between the granules. Chloroplasts axile, with two 

 pyrenoids. 



Zygospore unknown. 



Length 4650 /u ; breadth 40-42 /LI ; breadth of 

 isthmus 9-5-12-3 thickness 26*5-28 u. 



