136 BRITISH DESMIDIACEJ2. 



3. Cosmarium taxichondriforme Eiclil. & Gutw. 



(PI. LVI, figs. 8-10.) 



Cosmarium taxichondriforme Eiclil. & Gutw. Nonn. Spec. Alg. Nov. 

 1894, p. 169, t. 4, f. 23 ; Nordst. Index Desm. 1896, p. 250. 



Cells rather small, as long as broad, circular-hexa- 

 gonal, deeply constricted, sinus narrow and slightly 

 open ; semicells pyramidate-semicircular, basal angles 

 very faintly produced and slightly thickened, generally 

 turned downwards. Side view of semicell subcircular, 

 with flattened apices. Vertical view elliptic with pro- 

 duced poles, ratio of axes 1:2. Cell- wall finely 

 punctate. Chloroplasts axile, each with one pyrenoid. 



Zygospore unknown. 



Length 31-41-5 p.; breadth 31-47 ft; breadth of 

 isthmus 10-15 /x,; thickness 17-22 p. 



ENGLAND.- -Bowness, Westmoreland ! 



Geogr. Distribution. Gralicia in Austria. 



In outward appearance this species bears considerable re- 

 semblance to Cosmarium taxiclwndrum Lund.,, but is easily 

 distinguished by the entire absence of surface granules and 

 by the presence of only one pyrenoid in the axile chloroplasts. 



It still more closely resembles a tropical species, C. nudum 

 (Turn.) Gutw. (= C. taxiclwndrum var. nudum Turn.), from 

 which it is distinguished by the single pyrenoid in each semi- 

 cell and by the attenuation of the poles of the vertical view. 

 It should also be compared with C. crassangulatum Borge 

 (' Siissw. Chlor. Archang/ 1894, p. 25, t. 2, f. 23). 



We have only observed this species from some small water- 

 lily pools near Bowness in the English Lake District. 



4. Cosmarium circulare Keinsch. 

 (PL LVI, figs. 11, 13, 14.) 



Cosmarium circulare Keinscb, Spec. Gen. Alg. 1867, p. 113, t. 22, C. I, f. 1 

 -4 ; Lund. Desm. Suec. 1871, p. 41 ; Wolle, Freshw. Alg. U.S. 1887, p. 

 28, t. 57, f. 37 ; Hansg. Prodr. Algenfl. B5hm. 1888, p. 249 ; De Toni, 

 Syll. Alg. 1889, p. 975 ; West, Alg. N. Yorks. 1889, p. 292 ; Alg. N. 

 Wales, 1890, p. 288; Alg. W. Ireland, 1892, p. 144; Nordst, Index 

 Desm. 1896, p. 73. 



Didymidium (Cosmarium) circulare Keinsch, Algenfl. Frank. 1867, p. 108, 

 t. 10, f. 2. 



Ursinella circularis Kuntze, Keris. gen. plant. 1891, p. 924. 



