180 BRITISH DESMIDIACE^l. 



Lough Deryadd, Armagh ! Slieve Donarcl and Slieve 

 Bearnagh, Down ! 



This species is distinguished at once from C. tinctum Ralfs 

 by the form of its semicells both in the front and the vertical 

 view. 



It differs from C. abbreviatum Eacib. in its smaller size, its 

 different sinus, its relatively greater length, in the form of 

 its semicells, the slight central protuberance of the vertical 

 view, and the colour of its cell-wall. From C. pseudobiremum 

 Boldt, it is distinguished by the form of its semicells, having 

 the apex more truncate, by the less tumid vertical view, by 



its smaller size, and by the reddish-brown cell-wall. 







35. Cosmarium subretusiforme West & GL S. West. 



(PL LXII, fig. 19.) 



Cosmarium subretusiforme West & Gr. S. West, New Brit. Freshw. Alg. 

 1894, p. 5, t. 1, f. 20 ; Nordst. Index Desm. 1896, p. 247. 



Cells very minute, 1J times longer than broad, 

 moderately constricted, sinus open and obtuse ; semi- 

 cells subrectaiigular, basal angles broadly rounded, 

 upper part of sides retuse, upper angles acute, apex 

 broadly truncate and straight. Side view of semicell 

 elliptic- subcircular. Vertical view elliptic with sub- 

 acute poles, ratio of axes about 1 : 2'2. Cell- wall 

 smooth. 



Z ygospore unknown . 



Length 7'S-8ju; breadth 6'2-6'5/x,; breadth of apex 

 5*5 ju, ; breadth of isthmus 4*5 JJL ; thickness o JJL. 



ENGLAND.- -Borrowdale, Cumberland ! 



This minute species approaches Cosmarium retusiforme 



(\Ville) Gutw. in its front view, but is distinguished by its 

 much smaller size, its broader apices, and its different side 

 and vertical views. 



36. Cosmarium retusiforme (Wille) Gutw. 

 (PL LXII, figs. 17, 18.) 



Cosmarium Hammeri Eeinsch var. retusiforme Wille, Norges Ferskv. Alg. 



1880, p. 32, t. 1, f . 16. 

 C. retusiforme (Wille) Gutw. Wahr. d. Prioritat, 1890, p. 69; Flor. Glon. 



Okolic Lwowa, 1891, p. 55, t. 2, f. 12. 



