EUASTKUM. 9 



p. 182; Wolle, Desm. U. S. 1884, p. 99, t. 28, f. 12-13; Cooke, Brit. 

 Desiu. 1886, p. 66, t. 32, f . 3 ; De Toui, Syll. Alg. 1889, p. 1090 ; West, 

 Alg. W. Ireland, 1892, p. 137 ; Alg. Eng. Lake Distr. 1892, p. 722 ; 

 Eoy. & Biss. Scott. Desiii. 1893, p. 177 ; Nordst. Index Desni. 1896, 

 p. 141 ; West & G. S. West, Alg . S. England, 1897, p. 483 ; Alga-fl. 

 Yorks. 1900, p. 61. 



E. humerosum a. genuinum Eacib. Noun. Desni. Polon. 1885, p. 93. 



E. pinnatum Balfs b. intermedium Eacib I.e. p. 93, t. 13, f. 4. 



Hclierella humerosa Kuntze, Eevis. gen. plant. 1891, p. 898. 



Tells of moderate size, rather less than twice as 

 long as broad, deeply constricted, sinus narrowly 

 linear and dilated at the apex; semicells five-lobed, 

 incisions between the lobes widely open, upper in- 

 cisions deeper and less widely open than lower incisions ; 

 polar lobe dilated, almost anvil- shaped with rounded 

 angles, apex convex, straight, or even slightly retuse, 

 with a fairly deep and narrow median incision ; upper 

 lateral lobes mamillate or narrowly mamillate, directed 

 upwards and outwards ; lower lateral lobes subquadrate, 

 with retuse margins and rounded angles ; semicells 

 with three prominent protuberances across the base 

 and two smaller ones across the middle. Vertical 

 view elliptic, with three prominent protuberances on 

 each side. Cell-wall punctate. 



Zygospore unknown. 



Length 1 10-1 23 /x; breadth 65-75 ^ ; breadth of 

 isthmus 15'5 22 p. ; thickness 40 /x. 



ENGLAND. Blea Tarn, Westmoreland ! Pilmoor, 

 N. Yorks ! Xew Forest, Hants (Ralfs). Near Bovey 

 Tracey, Devon (Bennett). Halgavor Moor, Cornwall! 



WALES. Llyii Padarn !, Llvn-v-cwm-ffvnon !, and 



/ J V f / 



near Bettws-y-coed (Eoy), Carnarvonshire. Dolgelly, 

 Merioneth (Ra Ifs) . 



SCOTLAND. Ross ! Inverness, Aberdeen ! Kincar- 

 dine, Forfar, Perth, Argyll, Arran (Eoy fy Bissett). 



IRELAND. Lough Guitane and Carrantuohill, Kerry ! 

 Dublin and Wicklow (Archer). 



Geogr. Distribution. France. Germany. Austria 

 and Galicia. Xorwav. Sweden. Finland. Poland. 



t/' 



Faeroes. India. United States. 



E. Immerosum is the rarest of the larger British species of 

 Euastrum. It is subject to considerable variation in the 



