8 BRITISH DESMIDIACE^. 



Cosmarium Gayanum De Toni, Syll. Alg. 18S9 (July), p. 994; Gutw. Flor. 



Glon. Okolic Lwowa, 1891, p. 53 ; Flor. Glon. Okolic Tarnapola, 1894, 



p. 94. 



C. Gayii Gutw. Wahr. d. Prioritat, 1890, p. 69. 

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



Cells large, in general outline elliptic, about 1^ times 

 as long as broad, deeply constricted, sinus narrowly 

 linear with a slightly dilated extremity; semicells 

 ovate-pyramidate from a flat base, basal angles sub- 

 rectangular but obtuse, sides convex, in the upper part 

 rather rapidly converging to the somewhat narrow and 

 subtruncate apex. Side view of semicell elliptic. 

 Vertical view elliptic, ratio of axes about 1 : 1*6. Cell- 

 wall finely granulate, granules arranged in radiating 

 and subconcentric series, about 12 visible on each 

 lateral margin and 4 at the apex. Chloroplasts axile, 

 with two pyrenoids in each semicell. 



Zygospore globose, furnished with numerous, short, 

 rather stout processes (about 21 visible around the 

 periphery) ; apex of each process 2-3-denticulate. 



Length 1 70-90 /*; breadth 48-64 p; breadth of 

 isthmus 16-19 JIG; thickness 30-36 /x; diam. zygosp. 

 without processes 60 /x, with processes 95 /x. 



Geogr. Distribution. --France. Galicia in Austria. 



C. Gayanum is almost of the same outward form as C. 

 pyramidatum, but is at once distinguished by its granulate 

 cell-wall. The granules are very small and disposed in. a 

 very characteristic manner. The typical form has not been 

 observed in the British Islands. 



Var. eboracense nob. (PL XCIII, figs. 6-8.) 



C. eboracense West, Alg. N. Yorks. 1889 (October), p. 292, t. 291, f. 4; 

 Alg. W. Ireland, 1892, p. 155 ; Eoy & Biss. Scott. Desm. 1894, p. 100 j 

 West & G-. S. West, Alga-fl. Yorks. 1900, p. 82. 



Granulation of semicells denser, granules more 

 numerous (19-23 visible on each lateral margin); apex 

 obscurely 4-6 granulate, rarely smooth and very faintly 

 concave ; granules in the centre of the semicells con- 

 siderably reduced. 



Length 90*5-1 10 ft; breadth 55-68 /x; breadth of 

 isthmus 20-22 jit; thickness 39-41 p.. 



