Freshwater Algae 27 a 



Cosmarium tetraophthalmum Br^b. 



This large, universally distributed species was found only in the Hippuris 

 swamp at Herschel island, where it was in fair quantity. All specimens observed 

 were of full size and showed both the granulate and punctate character of the 

 wall clearly and the relatively smooth apex. 



Cosmarium trachypleurum Lund. var. minus Racib. (Plate IV, fig. 4) 



A small form of this variety occurred in a mixture of plankton and bottom 

 deposits, from a tundra pond, and also in a pond between the lake and sea at 

 Teller. 



Cosmarium Turpinii Br4b. 



This species was almost as common as C. Botrytis. It was found in the lagoon 

 lake at Teller and Demarcation point, and in the plankton and bottom samples 

 of the big lake and in the river bed at Bernard harbour. 



Cosmarium undulatumi Corda 



This species, although widely distributed in the world, is not generally 

 common. It was found by the expedition only at Bernard harbour, where it 

 occurred in a plankton collection and a general collection from the big lake. 



Xanthidium Ehrenb. 



This genus, which has numerous widely distributed species, was represented 

 by only three species, all from the Hippuris swamp at Herschel island. 



Xanthidium antilopaeum (Breb.) Ktitz. 



This was the commonest member of the genus. However, it was not very 

 plentiful. All specimens observed were quite normal and of average size. 



Xanthidium cristatum Br6b. var. bituberculatum nov. var. 



(Text fig. 4, a, b) 



A specie typica maxime distinctum semicellulis majoribus, paulo longioribus 

 quam lat., minus angulatis; area centralis tuberculis duobus munita; a vertice 

 ■^isae (semicellulae) eUipticae, lateribus bituberculatis. 



Cells slightly smaller than in the type, a little longer than broad. Sinus 

 open and deeply constricted. Vertical view elliptic. Semi-cell somewhat sub- 

 semicircular with a convex base furnished with spines as in the type, but less 

 angular at the spines. The central area is provided with two circular tubercles 

 in a line parallel to the long axis of the semi-cell. Apical view elliptical, showing 



6L. 



Fig. 4. Xanthidium cristatum Breb. var. hituhermlatum nov. var. X 500; a, face view, 6, end view. 



