COSMAEIUM. :, 



52. Cosmarium cymatopleurum Xordst. 

 (PL LXV, figs. 8, 9.) 



Cosmarium cymatopleurum Xordst. Desm. Spetsb. 1872, p. 28, t. 6, f. ! 

 Desm. Arctose, 1875, p. 18; Cooke, Brit. Desm. 1887, p. 188/t. 66 f 3 

 De Toni, Syll. Alg. 1889, p. 970 ; West, Alg. Engl. Lake Distr., 1892, p' 

 724 ; Lutkem. Desm. Attersees, 1893, p. 556 ; Xordst. Index Desmid. 

 1896, p. 96 ; West & O. S. West, Alga-fl. Yorks. 1900, p. 80. 



C. cymatopleurum forma polonica Bacib. Desm. Nowe, 1889 p 87 t 5 

 f. 36. 



Ursinella cymatopleura Kuntze, Revis. gen. plant. 1891, p. 924. 



Cells large, about 1-J- times longer than broad, 

 deeply constricted, sinus very narrow with a dilated 

 apex, opening outwards; semicells truncate- pyrami- 

 date, from a subreniform base converging upwards, 

 sides almost straight and very slightly undulate, upper 

 angles obtuse, apex very slightly produced, convexly 

 truncate, sometimes delicately undulate. Side view 

 of semicell elliptic-circular. Vertical view elliptic, 

 poles bluntly pointed (rarely rounded), with three 

 parallel series of undulations (interrupted in the 

 middle) more or less distinctly visible within each 

 lateral margin, ratio of axes about 1 : 1'66. Cell-wall 

 rather thick and finely punctate, often becoming 

 yellow. Chloroplasts axile, each with two pyrenoids. 



Zygospore unknown. 



Length 82-9 7 /u ; breadth 60-70 /u; breadth of apex 

 25-38 /i ; breadth of isthmus 25-30 /t; thickness 40- 

 43 ^1 ; thickness of cell- wall 2-2*5 n. 



ENGLAND.- -Xear Bowness, Westmoreland ! Peny- 

 ghent, W. Yorks ! fickle Fell, X. Yorks ! 



Geocjr. Distribution.- -Austria, Gralicia. Poland. 

 Finland. Spitsbergen. Nova Zembla. 



C. cymatopleurum and its varieties are essentially Alpine 

 Desmids, occurring amongst mosses on dripping rocks asso- 

 ciated with C. Bolmiense, C. anceps, C. speciosum, C. Et>-lm- 

 chautnse, Stauraztruni acarides, etc. These species are also 

 associated in boggy mountain springs, hut C. cymatopleurum 

 is perhaps the rarest of them and is only occasionally 

 found. 



