AKTHRODESMUS. 95 



but Heimerl's figures do not show the character upon which 

 \vi> have founded this variety. 



t 



Var. Ralfsii W. & G. S. West. (PL OXIV, fi^s. 



2-4.) 



Arthrodesmus Incus var. ft Ralfs, Brit. Desm. 1848, p. 118, t. 20, f. 4 e-li~ 



? A. Incus forma Brebissonii Eacib. Desm. Nowe, 1889, p. 96, t. 6, f. 15. 



A. Ralfsii Wes% Alsf. W. Ireland, 1892, p. 168 ; Alg. Engl. Lake Distr. 

 1892, p. 730; W. & G. S. West, Alg. S. England, 1897, p. 497. 



A. Incus var. vulgaris Eichl. & Kacib. iiiRospraw. Spraw. Wydz. matem.- 

 przyr. Akad. Umiej. Krakow, xxvi, 1893, p. 119. 



A. Incus var. Ralfsii W. & G. S. West, Alga-fl. Yorks. 1901, p. 109 ; Alg. 

 N. Ireland, 1902, p. 58 ; Scott Freshw. Plankton, I. 1903, p. 528 ; Freshw. 

 Alg. Orkneys and Shetlands, 1905, p. 23 ; Cushman in Ehodora, vii, 

 1905, p. 261 ; W. & G-. S. West, Further Contrib. Freshw. Plankton 

 Scott. Lochs, 1905, p. 485 ; Cushman in Bull. Torr. Bot. Club, xxxiii, 

 1907, p. 613 ; W. & G. S. West, Brit. Freshw. Phytoplankton, etc., 1909, 

 p. 181 ; Phytoplankton Engl. Lake Distr. 1909, p. 138. 



? Staurastrum Sarsii var. longispinum Huitfeldt-Kaas, Plankton. Norske 

 Vande, 1906, p. 56, t. 1, f. 18, 19. 



Semicells trapeziform, with the sides somewhat 

 upwardly diverging and a straight or slightly concave 

 apex. Sinus a small rounded excavation. Spines 

 of moderate size and slightly convergent. 



Zygospore globose, furnished with long, simple 

 spines. 



Length 27-33/x ; breadth without spines 18-20/x, with 

 spines 44-47 /x; breadth of isthmus 7'5-9'5/^; diam. 

 zygosp. without spines 19 /*, with spines 35 p.. 



ENGLAND. Westmoreland ! AY., X., and E. Yorks ! 



AYarwicks ! Essex ! Surrey ! Devonshire ! Cornwall ! 



t/ 



In the plankton of Codale and Easdale Tarns, West- 

 moreland ! 



WALES.- -Capel Curig, and in the plankton of Llyn 

 sf wen, Carnarvonshire ! 



o ' 



SCOTLAND.- -Perth ! Aberdeen ! Inverness ! Forfar ! 

 Sutherland ! In the plankton of Loch Fadaghoda, 

 Loch Eoinebhall, and Loch Shubhaill, Lewis; and 

 Loch a Bhursta, Benbecula, Outer Hebrides ! Orkneys ! 



IE ELAND.- -Donegal ! Eoundstone and Lough Derry- 

 clare, Galway ! Near Louo-h Briii, Kerry ! Castletown 



V / 



and Adrigole, Cork ! 



Geogr. Distribution.- -Sweden. Greenland. (Consult 

 also the distribution given under the type.) 



