28 A Canadian Arctic Expedition, 1913-1918 



two tubercles on each side. Length without spines 64-68m, with spines 78-84^; 

 breadth without spines 50-53m, with spines 66-68^. Breadth of isthmus ^Um- 

 Tubercles diameter Spt, distance apart 9-11m- . , j • +u 



No cells were observed with a large central tubercle such as is tound in tne 

 type, and no other varieties were seen. It was not quite as numerous as the 

 preceding species. 



Xanthidium fasciculatum Ehrenb. 



This species was about as frequent as X. antilopaeum. Most of the plants 

 were slightly below average size. 



Arthrodesmus Ehrenb. 



Arthrodesmus Incus (Breb.) Hass. var. Ralfsii W. & G. S. West forma 

 subhexagona W. & G. S. West (Plate III, fig. 14) 



This was the only representative of the genus. It is a world-wide species 

 with a considerable variation. It was fairly common in the collection from the 

 Hippuris swamp at Herschel island, and all specimens seen were small, short 

 spined, sub-hexagonal forms characteristic of the forma subhexagona of the 

 var. Ralfsii. 



Staurastrum Meyen. 

 Staurastrum Avicula Br6b. (Plate IV, fig. 13) 



This species was frequent in a mixed collection of plankton and bottom 

 deposits from the tundra pond at Teller. 



Staurastrum Br6bissonii Archer (Plate IV, fig. 12) 



A form of this species was not infrequent in the lake at Teller. It differed 

 from the type in having the spines at the angles shorter than usual. 



Staurastrum brevispinum Bail. 



This species was rather rare and was found only in the plankton from the 

 big lake at Bernard harbour. 



Staurastrum brevispinum Bail. var. inerme Wille 



I was uncertain at first as to the exact determination of this desmid, so I 

 submitted some drawings to the late Professor G. S. West, and he identified it 

 as this variety. It was fairly abundant in the lake at Teller. Previous records 

 are known from Nova Zembla, England, and the United States of America. 



Staurastrum denticulatum Archer 



This species was also fairly abundant at Teller, in the lagoon lake, along 

 with other algae. It was also found a few times in the plankton. Although a 

 fairly common species it was not found in any other locality. 



Staurastrum furcigerum Br6b. (Plate IV, fig. 9) 



Only a few empty semi-ceUs of this species were observed, and they were 

 all in the material from the. Hippuris swamp, Herschel island. With one 

 exception they were all triangular forms and true to type. One semi-cell was 

 abnormal, bearing, in addition to the usual pair of arms at each angle, a seventh 

 arm or process arising in the middle of one side. The species is not uncommon 

 in arctic regions. 



