104 BRITISH DESMIDIACE^E. 



Cells minute, about as long as broad, deeply con- 

 stricted, sinus open and subrectangular, with an acu- 

 minate apex ; semicells obversely subsemicircular (or 

 elliptic-cuneate with convex sides which widely diverge 

 upwards), angles slightly produced and obtuse, apex 

 very broad and slightly convex, with a small wart in 

 the centre of the semicell. Side view of semicell sub- 

 circular, with a minute protuberance at the middle on 

 each side. Vertical view rhomboid-elliptic, ratio of 

 axes about 1 : 1*5, with a small rounded wart at the 

 middle on each side, poles minutely produced. Cell- 

 wall thin and smooth. 



Zygospore unknown. 



Length 12-13 /A; breadth 12-13 p ; breadth of 

 isthmus 7 ^ ; thickness 9 ^. 



SCOTLAND.- -Loch Ruthven, Inverness; Dinnet, Birse- 

 more Loch, and south side of Birsemore, Aberdeen 

 (Roy fy Bis sett). 



Geogr. Distribution . Norway. 



We have not seen this species. Perhaps it is nearly related 

 to C. Sphagnicolum. 



115. Cosmarium Thwaitesii Half's. 

 (PL LXXIII, figs. 27, 28.) 



Cosmarium Thwaitesii Ralfs, Brit. Desm. 1848, p. 109, t. 17, f . 8 ; Arch, in 



Pritch. Infus. 1861, p. 735 ; Rabenh. Flor. Europ. Alg. Ill, 1868, p. 175; 



Lund. Desm. Suec. 1871, p. 47, 52 ; West, Alg. W. Ireland, 1892, 



p. 163 ; Alg. Engl. Lake Distr. 1892, p. 729; Roy & Biss. Scott. Desm. 



1894, p. 176 ; Gutw. Flor. Glon. Okolic Tarnapola, 1894, p. 83 ; Nordst. 



Index Desm. 1896, p. 254 ; West & G. S. West, Alg. S. England, 1897, 



p. 492 ; Alga-fl. Yorks. 1900, p. 94. 

 Dys-phinctium Thwaitesii Reinsch, Algeiifl. Fraiiken, 1867, p. 177 ; De Toni, 



Syll. Alg. 1889, p. 890. 



Cosmariuvti Thwaitesii a. typicum Klebs, Desm. Ostpreuss. 1879, p. 26. 

 Calocylindrus Thwaitesii (Ralfs) Schaarschm. in Magyar Novell. Lapok. 



vi, 1882, p. 73 ; ? Wolle, Desm. U. S. 1884, p. 56, [t. 12, f. 19], t. 50, f . 28 ; 



Cooke, Brit. Desm. 1887, p. 126, t. 44, f . 5 ; West, Alg. N. "Yorks. 1889, 



p. 293 ; Alg. N. Wales, 1890, p. 291. 



Cells of moderate size, 2-2-| times as long as broad, 

 slightly constricted ; semicells oblong or subelliptic- 

 oblong, sides subparallel, slightly convex, and very 

 faintly converging upwards, apex rounded or slightly 



