STAURASTRUM. 17 



1901, p. 232, t. 8, f. 1 ; West & G. S. West, Scott. Freshw. Plankton, I, 

 1903, p. 543, t. 17, f. 1-4; Further Contrib. Freshw. Plankton Scott. 

 Lochs, 1905, p. 485, t. 1-5 ; Comp. Study Plankton Irish Lakes, 1906, 

 p. 103, t. 11, f. 17-19; Brit. Freshw. Phytoplankton, 1909, p. 168; 

 Phytoplankton Engl. Lake Distr. 1909, p. 189 ; Period. Phytoplankton 

 Brit, Lakes, 1912, p. 417. 



Arthrodesmus longicornis Roy & Biss. Scott. Desm. 1894, p. 28 (fornia 

 biradiata}. 



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

 constricted, sinus acute-angled, widening considerably ; 

 semicells roughly triangular, lateral margins convex, 

 and apex subconvex, the upper angles provided with 

 very long, strong and diverging spines. Vertical view 

 2-4-radiate, lateral margins convex, with a strong spine 

 at each angle. Chloroplast axile, with a central pyrenoid 

 and a pair of lobes stretching into each angle. 



Zygospore unknown. 



Length, without spines, 20-31 \L ; breadth, without 

 spines, 14-22 pt ; length of spines 15-38pL ; breadth of 

 isthmus 5*5-8 \L ; thickness (in forma brradiata) 12'5- 

 14 JJL. 



ENGLAND. Plankton of Buttermere, Crummock 

 Water, Ennerdale (f . 2-radiata) and Wast Water, Cumber- 

 land ! Plankton of Brother's Water, Red Tarn (f. 2- 

 and 3-radiata3), Hawes Water, Codale Tarn, Easedale 

 Tarn, and Windermere, Westmoreland ! 



WALES.- -In the plankton (f. 2-radiata). Llyn Cwlyd, 

 Carnarvonshire ! 



SCOTLAND. --Fairly general in the plankton of the 

 mainland (both 2- and 3-radiate forms), of the outer 

 Hebrides, and of the Orkneys and Shetlands ! 



IRELAND.- -Lough Guitane, and common in the plank- 

 ton, Co. Kerry ! Rare in the plankton of Lough Keel, 

 and Lough Gall (f. 2-radiata), Co. Mayo ! 



Geogr. Distribution. --Noiw&y. Finmark. Finland. 

 Faeroes. Greenland. Guiana. 



St. jaculiferum is almost entirely confined to plankton, or is 

 otherwise an inhabitant of large lakes. In some of the lakes in 

 S.W. Ireland and W. Scotland it forms a very prominent feature 

 of the plankton, and it is also fairly general in the plankton of 

 the Welsh, lakes, and of the English Lake District, but is apparently 



VOL. V. 2 



