36 BRITISH DESMIDIACE^E. 



Var. sibiricum Boklt. (PI. LXVIII, figs. 17, 18.) 



C. Novse-Semlix var. sibiricum Boldt, Siber. Chlorophy. 1885, p. 108, t. 5, 

 f. 14 ; West & G. S. West, Alg. S. England, 1897, p. 487. 



A distinct variety with a deeper sinus and narrower 

 isthmus ; apex of semicells retuse-emarginate ; denti- 

 culations round the lateral margins prominent, and 

 only very few (2 or 3) within each margin ; vertical 

 view more narrowly elliptic. 



Length 17 -18 /JL; breadth 15-1 5*5 /A; breadth of 

 isthmus 6 8 5-7fi; thickness 9*5-10 /i. 



ENGLAND.- -New Forest, Hants! (very abundant in 

 Ashurst Bog, June, 1897). 



Geogr. Distribution.- -Siberia. 



69. Cosmarium Regnesi Reinsch. 

 (PL LXVIII, figs. 19-28.) 



Cosmariiim Regnesi Reinsch, Spec. Gen. Alg. 1867, p. 116, t. 22 A III, 

 f. 1-5 ; Coiitrib. Alg. et Fung. 1875, p. 89, t. 10, f. 12 ; Turn. Notes 

 Freshw. Alg. 1886, p. 34, t. 1, f. 10 ; Cooke, Brit. Desm. 1886, p. 95, 

 t. 42, f. 19 ; De Toni/Syll. Alg. 1889, p. 961 ; West, Alg. N. Wales, 1890, 

 p. 289 ; Alg. W. Ireland, 1892, p. 149 ; Alg. Engl. Lake Distr. 1892, 

 p. 726 ; Roy & Biss. Scott. Desm. 1894, p. 173 ; West & G. S. West, Alo-. 

 Madag. 1895, p. 59, t, 6, f. 44 ; New and Int. Freshw. Alg. 1896, p. 155, 

 t. 3, f. 30, 31 ; Nordst. Index Desm. 1896, p. 222 ; West & G. S. West, Alg. 

 S. England, 1897, p. 487 ; G. S. West, Variation Desm. 1899, p. 387, 

 t. 10, f. 10, 12-17 ; West & G. S. West, Alga-fl. Yorks. 1900, p. 89 ; 

 Alg. N". Ireland, 1902, p. 36 [inclus. var. montanum] ; Freshw. Alg. 

 Orkneys and Shetlands, 1905, p. 22. 



Didymidium (Cosmarium) Regnesi Reinsch, Algenfl. Franken, 1867, p. 112, 

 t. 7, f. 8. 



Ursinella Regnesi Kuntze, Revis. gen. plant. 1891, p. 925. 



Cells very small, about as long as broad, deeply con- 

 stricted, sinus open, rounded, and widely excavated ; 

 semicells transversely oblong-rectangular with six 

 (rarely with, eight) minute marginal teeth, which are 

 generally more or less equidistant, two apical and two 

 lateral, apex (between the apical teeth) widely retuse. 

 Side view of semicell subcircular-elliptic. Vertical 

 view elliptic, ratio of axes about 1 : 2. Cell-wall 

 smooth. Chloroplasts axile, with one central pyrenoid. 



Zygospore generally rhomboid, with the sides slightly 

 concave and the angles rounded; sometimes rounded- 



