26:2 BIUTISH DESMIDIACE.K. 



Cell- wall rather thick and smooth. Chloroplasts axile, 

 with one pyrenoid. 



Zygospore unknown. 



_Length 40-43 p.; breadth 28-32 p.; breadth of apex 

 17 '6 p. ; breadth of isthmus 1 2-13*5 jn; thickness 20 /A. 



SCOTLAND. Powlair and Heuo-hhead near Abovne, 



. ** 



Aberdeen ; Crathes and Dnrris, Kircardine (Roy 



Bissett) . 



IRELAND. --Castletowii, Kerry ! 



Geocjr. Distribution.- -Gralicia in Austria (var.). 

 X. Sweden. Bornholm. Poland (var.). United 

 States. 



This species should he compared with C. retusum (Perty) 

 Eabenh. Eaciborski ('Desm. Xowe/ 1889, p. 82, t. 5, f. 17) 

 has described a " var. tatricum" of C. eductum which does 

 not appear to us to differ in any essential point from the 

 typical plant. 



218. Cosmarium didymochondrum Nordst. 



(PI. XC, fig. 10.) 



Cosmarium didymochondrum Nordst. Desni. Ital. 1876, p. 36, t. 12, f. 11 ; 



De Toni, Syll. Alg. 1889, p. 972 ; Eacib. Desm. Nowe, 1889, p. 87 ; Eoy 



& Biss. Scott, Desm. 1894, p. 45 ; West & G. S. West, Alga-fl. Yorks. 



1900, p. 84; Borge in Ber. Scliweiz. bot. Gcs. 1901, p. 104 c, fig. [forma]; 



Alg. Argentina u. Boliv. 1906, p. 8. 

 Ursinella didymochondra Kuntze, Eevis. gen. plant. 1891, p. 924. 



Cells somewhat small, about 1-J times as long as 

 I>road 5 deeply constricted, sinus narrowly linear with a 

 slightly dilated extremity ; semicells sub semicircular- 

 quadrate, of the same width from the broad base to a 

 little above the middle, then very gradually narrowed 

 to a somewhat produced apex, sides 5-7-crenate, lower 

 crenations small and rather indistinct, basal angles 

 rectangular but obtuse, upper crenations distinct and 

 larger, apex truncate and indistinctly 4-undulate ; 

 within the margin with two (rarely three) concentric 

 series of granules (often very indistinct) ; in the centre 

 immediately adjacent to the isthmus with two granules. 

 Side view of semicell ovate. Vertical view elliptic, in 

 the centre smooth. Cell-wall minutety punctate and 



