M1CBASTERIAS. 81 



W. Ireland, 1892, p. 133; Roy & Biss. Scott. Desm. 1893, p. 174; 

 Johnson, Species of Micrasterias, 1894, p. 58, t. 6, f. 5, 6 ; Nordst. Index 

 Desm. 1896, p. 201 ; West. & G. S. West, Some N. Amer. Desm. 1896, 

 p. 238, t. 13, f. 28; Alg. N. Ireland 1902, p. 30; Scott. Fresh w. Plank- 

 ton, I, 1903, p. 526. 



Enastrum didymacanthum Nag 1 . Gait, einzell. Alg. 1849, p. 123, t. GH, f. 1. 



Tetrachastrum pinnatifidum Dixon in Quart. Journ. Micr. Sci. 1859, p. 83 ; 

 Arch, in Pritch. Infiis. 1861, p. 725. 



Didymidium (Micrasterias) pinnatifidum Eeinsch. Algenfl. Frank. 1867, 

 p. 141. 



Micrasterias oscitans Ralfs var. pinnatijtda Rabenh. Flor. Europ. Alg. Ill, 

 1868, p. 189 ; Hansg. Prodr. Algenfl. Bohni. 1888, p. 208 ; DeToni,' 

 Syll. Alg. 1889, p. 1110; Liitkem. Desm. Attersees, 1893, p. 562. 



Holocystis pinnatifida Bennett, Freshw. Alg. Eng. Lake Distr. 1886, p. 8. 



Cells small, a little broader than long', deeply con- 

 stricted, sinus open, triangular-acuminate with a 

 narrowed apex ; semicells 3-lobed, the interlobular in- 

 cisions deep and broadly rounded; lateral lobes hori- 

 zontally disposed, semifusiform, with attenuated and 

 minutely bifid apices ; polar lobe widely spreading, 

 extremities narrower than those of the lateral lobes 

 and minutely bifid, apex convex, straight, or sometimes 

 very slightly retuse. Side view of semicell narrowly 

 ovate-pyramidate, with a rounded apex. Vertical view 

 narrowly rhomboid-lanceolate, with acuminate poles. 

 Cell-wall very minutely punctate. 



Zygospore globose, furnished with long, stout, acute 

 spines, each arising from a blunt protuberance. 



Length 53-76 p ; breadth 57-80 /t; breadth of polar 

 lobe 39-5 7 /u; breadth of isthmus 12-18 /n ; thickness 

 16-18 ILL; diam. zygosp. without spines 44 /x, with 

 spines 67 /LI. 



ENGLAND. Ambleside (Ralfs) and Bowness (Bissett), 

 Westmoreland. 



WALES.- -Capel Curig, Carnarvonshire (Coolie fy 

 Wills). Dolgelly, Merioneth (Ralfs). 



SCOTLAND. General, but scarce (Eoy fy Sissett). 

 Aberdeen ! Inverness ! Scourie and Khicoiiich, 

 Sutherland ! Fairly general in Lewis and Harris ! 

 Plankton of Loch Fadaghoda, Lewis, and of Loch 

 Xan Eun, K. Uist ! 



IRELAND. Near Grlenties and Lough Anna, Donegal ! 

 Ballynahinch, Roundstone, Loughs Aunierin, Athry, 



VOL. II. 6 



