46 BRITISH DESMIDIACE.E. 



towards the apex, and retuse, apex truncate and 

 retuso-emarginate. Side view of semicell quadrate- 

 rectangular, with attenuated poles which are o-crenu- 

 late. Vertical view subrectangular, with slightly 

 convex sides, poles broadly truncate and 3-crenulate. 

 Cell-wall smooth. 



Zygospore unknown. 



Length 32-39 //,; breadth 20-23 p.; breadth of isth- 

 mus 7'5-8'5/x; thickness 11-16 p. 



ENGLAND.- -Westmoreland (Bissett). Mickle Fell, 

 N. Yorks ! Hants, Devon, and Cornwall (Bennett). 



WALES. Capel Curig and Pen-y-gwrydd, Carnarvon- 

 shire (Roy). 



SCOTLAND. Ross, Inverness !, Aberdeen, Kincardine, 

 Forfar, Perth, Argyll and Arran (Roy fy Bissett). 



IRELAND.- -Dublin and Wicklow (Archer). 



Georjr. Distribution. Germany. Portugal. Norway. 

 Sweden. India (form). Central Africa. United States. 



E. erosum differs from E. dubium in. the character from 

 which the species derives its name, viz., the crenulated poles 

 of the side and vertical views. It is also less lobecl, with a 

 less deep apical incision, and is completely destitute of any 

 granulation on the surface. 



O 



29. Euastrum pulchellum Breb. 

 (PI. XXXVIII, figs. 14, 15.) 



Euastrum pulchellum Breb. Liste Desm., 1856, p. 124, t. 1, f . 5 ; Arch, in 

 Pritcli. Infiis., 1861, p. 730; Eabenh. Flor. Europ. Algar. Ill, 1868, 

 p. 186; De Toni, Syll. Alg. 1889, p. 1106; Roy. & Biss. Scott. Desin. 

 1893, p. 177 ; Nordst. Index Desm. 1896, p. 211 ; West & G. S. West, 

 Alga-fl. Yorks, 1900, p. 63 ; Alg. N. Ireland, 1902, p. 29. 



Helierella pulchella Kuntze, Revis. gen. plant. 1891, p. 899. 



Cells small, about 1^ times longer than, broad, very 

 deeply constricted, sinus narrowly linear with a slightly- 

 dilated extremity ; semicells more or less three-lobed, 

 with a shallow sinus between the lobes; polar lobe 

 widely rectangular-oblong, apex truncate with a deep 

 and narrow median incision, apical angles furnished 

 with a short diverging spine; lateral lobes rounded 



