148 BRITISH DESMIDIACE.E. 



Forma duplo-major Lund. (PI. XCIV, fig. 3.) 



C. excavatum Nordst. forma duplo-major Lund. Desni. Suec. 1871, p. 46 ; 

 Wille, Ferskv. Alg. Nov. Semlja, 1879, p. 47. 



Cells twice the size of the typical form. 

 Length 39-42'5/x,; breadth 21-5-25 //,; breadth of 

 isthmus 1 51 7 /A. 



WALES. --Capel Curig, Carnarvonshire! 

 Geogr. Distribution.- -Sweden. Nova Zembla. 



Except for its mucli larger size this form agrees very 

 closely with the original Brazilian C. excavatum. It is of the 

 same length as C. isthmium, but differs from that Desmid in 

 its proportionately narrower cells, its shallower constriction, 

 its broader isthmus, and in the disposition of its granules. 



148. Cosmarium subexcavatum West & G-. S. West. 



(PI. LXXVII, fig. 13.) 



Cosmarium excavatum Nordst. var. ellipticum Wille, Ferskv. Alg. Nov. 



Semlj. 1879, p. 47, t. 13, f. 46; ? Boldt, Desm. Gronlaiid, 1888, p. 28; 



Borg-. Ferskv. Alg. Ostgronl. 1894, p. 15. 

 C. excavatum Nordst. forma major Boldt, Desm. Gronlaiid, 1888, p. 28, t. 2, 



f. 30. 



C. isthmium West var. Willei West, Alg. W. Ireland, 1892, p. 160. 

 Dy sphinctium Willei Schmidle, Alg. Bern. Alp. 1894, p. 94. 

 Cosmarium subexcavatum, West & (i. S. West, Notes Alg. II, 1900, p. 293. 

 C. Willeanum Mignla in Flora von Dentschland, Osterreicli nnd der 



Schweiz. Bd. 5 (Desmidiacese in parts 29-36), 1906, p. 454, t. 23 N, f. 7. 



[Not C. Willeanum Eacib., 1892.] 



Cells small, about If times as long as broad, 

 moderately constricted, sinus open and subrectangular; 

 semicells subcircular (periphery about f to f of a 

 circle), cell- wall granulate, granules densely arranged 

 in longitudinal series [according to Wille's brief 



o L O 



description], 15-16 showing at the margin. Vertical 

 view circular or circular-elliptic. Chloroplasts axile, 

 one in each semicell, with a central pyrenoid. 



Zygospore unknown. 



Length 28*8-29 /x; breadth 19'2-23/x; breadth of 

 isthmus 10-8-11-0/*; thickness 19*2-20 p. 



Geogr. Distribution.- -Nova Zembla. Greenland. 



We have not seen any form exactly corresponding to the 

 Desmid described by Wille as " C. excavatum var. ellipticum" 

 Wille also describes the granules as disposed in longitudinal 

 series, and figures them in concentric series (consult PI. 



