EUASTRUM. 41 



E. bidentatum Xag\ is a species well differentiated from 

 E. elegans by its lobulate margins,, its larger and more de- 

 pressed apices, and its ornamentation. It is also larger than 

 most forms of E. elegans, although it is connected with that 

 species by E. elegans var. NOV& Semliex and E. elegans var. 

 ornatum. 



It is generally distributed all over the British Islands, and 

 retains its distinctive characters in a very constant manner. 



Almost the only variation met with is in the form of the lateral 



/ 



lobules and in the disposition of the surface ornamentation. 

 The central protuberance varies much in the number and 

 arrangement of its granules. The figures given by Xageli 

 are fairly good in outline, but he does not indicate the 

 markings which are always present on this species. 



Most probably the figure of E. elegans in RalfV 'Brit. 

 Desm./ t. 14, f. 7a, is a form of this species. 



25. Euastrum pictum Borg. 

 (PI. XXXVIII, fig. 1.) 



Euastrum pictum Borg. Desm. Brasil. 1890, p. 34, t. 3, f. 19. 



Cells relatively small, a little more than 1-J- times 

 longer than broad, deeply constricted, sinus narrowly 

 linear with a dilated extremity ; semicells subquadrate, 

 three-lobed ; polar lobe short and much dilated, apex 

 convex and undulate, with an open median incision, 

 apical angles furnished with a short, strong spine; 

 lateral lobes bilobulate, upper lobule small and fur- 

 nished with two small teeth, lower lobule larger and 

 furnished with three small teeth ; semicells in centre 

 with a large granulate protuberance, and with smaller 

 granulate protuberances within each lateral lobule and 

 each half of the polar lobe. Vertical view elliptic, 

 poles denticulate, and with a median granulated pro- 

 tuberance on each side. 



Z y gospore unknown . 



Length 72 /n ; breadth 43 /t ; breadth of isthmus, 

 11 /i; thickness, 27 /n. 



. Distribution. Brazil. United States (var). 



Absolutely typical forms of E. pictum do not occur in the 

 British Isles. Those already recorded (consult West, 'Alg. 



