64 BRITISH DESMIDIACE.E. 



Kincardine, Forfar, Perth ! (Ry fy Bt'ssett). Outer 

 Hebrides ! Shetlands ! 



IRELAND. Donegal ! Mayo ! Galway ! Kerry ! Dublin 

 and Wicklow (Archer). 



Geoc/r. Distribution. France. Belgium. Germany. 

 Gralicia in Austria. Norway. Sweden. Denmark. 

 Bornholm. Poland. S. Russia. Faeroes. Greenland. 

 India, United States. W. Indies. Brazil. Paraguay. 



E. gemmatiim is one of the prettiest and most characteristic 

 species of the genus. It is widely distributed, but somewhat 

 scarce. 



38. Euastrum verrucosum Ehrenb. 

 (PI. XL, fig. 1.) 



Euastrum verrucosum Ehrenb., 1834 ; Infus. 1838, p. 162, t. 12, f. v ; 



Ralfs in Ann. Mag. Nat. Hist. 1844, p. 189, t. 6, f. 3; Hass. Brit. 



Freshw. Alg. 1845, p. 379, t, 91, f . 7 ; Ralfs, Brit. Desm. 1848. p. 79, t. 



11, f. 2; Arch, in Pritch. Infus. 1861, p. 728; Rabenh. Flor. Europ. 



Algar. Ill, 1868, p. 179 ; Delp. Desm. Subalp. 1873, p. 94, t. 6, f . 13-15 ; 



Kirchn. Alg. Scliles. 1878, p. 160 ; Wolle, Desm. U. S. 1884, p. 100, t. 26, 



f . 1, 5 ; Cooke, Brit. Desm. 1886, p. 63, t. 31, f . 1 ; Hansg. Prodr. Algeiifl. 



Bohm. 1888, p. 204 ; De Toni, Syll. Alg. 1889, p. 1066 ; West, Alg. W. 



Ireland, 1892, p. 136 ; Alg. Eng. Lake Distr. 1892, p. 722 ; Roy & Biss. 



Scott. Desm. 1893, p. 178 ; Nordst. Index Desni. 1896, p. 268 ; West & 



Gr. S. West, Alg. S. England, 1897, p. 483 ; Alga-fl. Yorks. 1900, p. 65 ; 



Alg. N. Ireland, 1902, p. 27 ; Scott. Freshw. Plankton, I, 1903, p. 525. 

 E. verrucosum a. typicum Racib. Nonn. Desm. Polou. 1885, p. 94. 

 E. verrucosum a. typicum Boldt, Desni. Gronland, 1888, p. 6. 

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



Cells moderately large, subhexagonal, a little longer 

 than broad, deeply constricted, sinus open for half its 

 length and then narrowly linear; semicellsthree-lobed, 

 interlobular incisions deep but open ; polar lobe widely 

 cuneate, angles rounded and granulate, apex deeply 

 retuse ; lateral lobes wider than polar lobe, cuneate and 

 bilobulate, lower lateral lobule subconical, rounded, 

 granulate and horizontally directed, upper lateral lobule 

 submamillate, granulate, upwardly and outwardly 

 diverging ; semicells with three large protuberances 

 across the broadest part, the central one being the 

 largest, each protuberance furnished with large wart- 

 like granules arranged in concentric circles. Cell-wall 



O 



granulate, granules most evident at the angles where 



