156 URITISH DESMIDIACEJ1. 



Cells of medium size, about 10 times longer than 

 their diameter, slightly curved, outer margin 35-40 

 of arc, inner margin a little concave, and slightly but 

 widely tumid in the middle, gradually attenuated to 

 the apices, which are obtusely rounded ; cell-wall 

 smooth and colourless; chloroplast with eight ridges 

 and a central series of 4 or 5 pyrenoids; terminal 

 vaeuoles with a number of moving granules. 



Zygospore unknown. 



Length 1 50-220 /x ; breadth 17'5-22'5/u. 



ENGLAND. Masham, near Rievaulx Abbey, and 

 Stokesley, N. Yorks ! Kingsbury Green, Middlesex! 

 Tremethick Moor, Cornwall ! 



(tnujr. Uixti-ilml'nni. France. Glalicia in Austria. 

 Central Africa (var.). 



:>:>. Closterium tumidum Johnson. 

 (PI. XIX, figs. 15-18.) 



Cluxti:niun ('"run Khrenb. var. /3 Ball's, lirit. Desm. 1848, p. 17(5, t. 3O, 



f. 6 a-e ; Roy A: Hiss. Scott. Desm. 1894, p. 24-1. 

 Cl. Cornu b. forma tumidu- Rabeiih. Flor. Europ. Al^ar. Ill, ISDN, p. 137 ; 



De Toni, Syll. Alg. 1889, p. S3I>. 

 Cl. Cornu Wille, Fevskv. Alg. Nov. Semlj. 1879, p. 59, t. 14, f. so. SI 



(inclus. f. mnjin- AVille) ; Wille, Norges Ferskv. Al^. 1880, p. 57, t. 2, 



I 1 . 38 ; West, Desin. Maine', 1888 ; Alg. N. Wales, 189O, p. 285. 

 Cl. linnidtuii Johnson, Rare Desm. U.S. II, 1895, p. 291, t, 239, f. 4; 



Nordst. Index Desm. 1890, p. 2(i2 ; West \ G. S. West, Some Desm. 



U.S. 189S, p. 2S4 ; Alga-fl. Yorks. 1900, p. 53 ; Chloropliy. Koh Chang, 



1901, p. lb'0, t. 2, figs. 3, 4. 



Cells rather small, 8-9 times longer than their 

 diameter, slightly curved, outer margin 28-58 u of arc, 

 inner margin broadly tumid in the middle, faintly con- 

 cave towards the extremities, gradually attenuated 

 towards the apices, which are truncately rounded and 

 of somewhat variable width ; cell- wall smooth and 

 colourless ; chloroplasts with four or six ridges, and 

 l-o pyrenoids ; terminal vaeuoles with only one mov- 

 ing granule. 



/vgospore subrectangular, with retuse sides; angles 

 produced and truncately rounded; viewed from the 

 side, elliptical. 



