206 BRITISH DESMIDIACE.E. 



187. Cosmarium furcatospermum West & Gr. S. 



West. 



(PL LXXXI, figs. 10, 11 ; PL LXXXIV, figs. 8-10.) 



Cosmarium furcatospermum West & G. S. West, New Brit. Freshw. Algee, 

 1894, p. i, t, 1, f . 13 ; Nordst. Index Desm. 1896, p. 126. 



Cells small, a little longer than broad, deeply con- 

 stricted, sinus linear ; semicells truncate-semicircular 

 or oblono'-subsemicircular, basal angles subrectanerular 



O J O O 



or slightly rounded, lateral margins 4-5-crenate- 

 granulate, apex widely truncate and 5-6 -undulate, 

 with two (rarely with one) series of small granules 

 within the whole margin, and with the central region 

 of the semicells smooth or most minutely punctate. 

 Side view of semicell subcircular. Vertical view 

 elliptic or oblong-elliptic, ratio of axes about 1 : 1'7, 

 sides smooth, poles undulate-granulate. Chloroplasts 

 axile, one in each semicell, with a central pyrenoid. 



Zygospore angular-globose, ornamented with short 

 slender spines (7 visible around the periphery) very 

 deeply bi- or trifurcate at the extremity. 



Length 18-22 /x; breadth 16'5-l9//,; breadth of 

 isthmus 5' 7-7 /A; thickness 9-11 ft; diam. zygosp. 

 without spines 23-25 /a, with spines 40-42 p.. 



SCOTLAND. --Orkneys ! 



IK-ELAND.- -Shores of Lough Xeagh ! 



This species is nearest to C. spJialerostichum Nordst., but 

 can be distinguished by the subundulate apices, the smooth 

 central area of the semicells, the narrower vertical view, and 

 the spiny zygospore. Moreover, the granules are rounded 

 and somewhat flattened, whereas the marginal granules of 

 C. spJialerostichum are acute. 



188. Cosmarium punctulatum Breb. 

 (PI. LXXXIV, figs. 13, 14; PI. Oil, fig. 22.) 



Cosmarium punctulatum Breb. Liste Desm. 1856, p. 129, t. 1, f. 16 ; 

 Kabenh. Flor. Europ. Algar. Ill, 1868, p. 157 ; Lund. Desra. Snec. 1871, 

 p. 30 ; Wittr. Gotl. Ol. sotv. Alg. 1872, p. 57 ; Nordst. Norges Desm. 

 1873, p. 14 ; Kirclm. Alsr. Scliles. 1878, p. 148 ; ? Wolle, Desm. U. S. 

 1884, p. 74, t. 13, f. 4 ; ? Cooke, Brit. Desm. 1887, p. 104, t, 42, f. 7 ; 



