170 BRITISH DESMIDIACE.E. 



27. Cosmarium flavum Roy & Biss. 



(PI. LXI, figs. 21, 22.) 



Cosmarium flavum Eoy & Biss. Scott. Desm. 1894, p. 101, t. 2, f. 17 : 

 Nordst. Index Desni. 1896, p. 124. 



Cells rather small, about as long as broad, deeply 

 constricted, sinus narrow towards the apex but opening 

 outwards ; semicells elliptic-oblong with a somewhat 

 flattened apex. Side view of semicell subglobose. 

 Vertical view elliptic, ratio of axes about 1 : 1*7. Cell- 

 wall smooth and of a yellow colour. 



Zygospore globose and smooth. 



Length 32/x; breadth o2/x; breadth of isthmus 

 10 fji ; thickness 15'5 JJL ; diam. zygosp. 40 ft. 



SCOTLAND. Loch Inver, Sutherland; Scotston, 

 Birsemore, Craigendinnie, Dinnet, Dawin, Auchnerran, 

 and Grlen Clunie, Aberdeen ; Crathes, Cammie, and 

 Dalbrake, Kincardine (Roy $ Bissett). 



We have not seen this species, which. Roy & Bissett record 

 as " rare " in Scotland. It appears to he very closely related 

 to Cosmarium contractum forma Jacobsenii and C. contractual 

 var. ellipsoideum, from each of which it chiefly differs in the 

 cells being more flattened at the apices and in the yellow tint 

 of the cell-wall. 



28. Cosmarium contractum Kirchn. 



(PI. LXI, figs. 23-25, 34.) 



Cosmarium contractum Kirchn. Alg. Schles. 1878, p. 147 ; Wolle, Desm. 



U.S. 1884, p. 63, t. 16, f. 1 ; t, 50, f. 24 ; De Toni, Syll. Alg. 1889, p. 949; 



West, Alg. N. Wales, 1890, p. 291 ; Alg. W. Ireland, 1892, p. 160 ; Alg. 



Eng. Lake Distr. 1892, p. 729 ; Eoy & Biss. Scott. Desm. 1894, p. 44 ; 



West & a. S. West, Alg. Madag. 1895, p. 70, t. 8, f . 5 ; Nordst, Index 



Desm. 1896, p. 80 ; West & G. S. West, Welw. Afric. Freshw. Alg. 1897, 



p. 175 ; Alg. S. England, 1897, p. 491 ; Freshw. Chlorophy. Koh Chang. 



1901, p. 91; Alga-fl. Yorks. 1900, p. 74; Alg. N. Ireland, 1902, p. 40; 



Scott. Freshw. Plankton I, 1903, p. 526; Further Contrib. Freshw. 



Plankton Scott. Lochs, 1905, p. 483. 



C. contractum a. silesiacum Racib. Xonn. Desm. Polon. 1885, p. 84. 

 Ursinella contracta Kuntze, Eevis. gen. plant. 1891, p. 924. 



Cells rather small, about 1-J times longer than broad, 

 very deeply constricted, sinus narrow towards the apex, 

 rapidly widening outwards; semicells sub-elliptic, 



