1923] 



MOORE AND CARTER — ALGAE FROM NORTH DAKOTA LAKES 401 



Plankton of Brush Lake; Long Lake, near Ruso; Lake Wil- 

 liams; Ensign Lake; Red Willow Lake. 



The dimensions of the present examples agreed very well with 

 those given by Lagerheim, but the information given by him is not 

 altogether complete. In the genus Holopedia the cells are usually 

 ellipsoid in form, with their long axis perpendicular to the plane 

 of the thallus. In the North Dakota specimens, however, the 

 cells were nearly spherical, being approximately the same size 

 in all three dimensions. Lagerheim states only the length and 

 breadth of the cells, and does not say whether or not the cells 

 were larger in the third dimension than the other two. The alga 

 was very common in the plankton of Brush Lake, and here the 

 colonies reached quite a considerable size. In the other localities 

 it was not nearly so abundant, and usually occurred in small 

 fragments. The species has previously been known only from 

 Europe. 



Genus tetrapedia Reinsch 



Tetrapedia Reinschiana Archer, Grevillea 1: 46. pi. 3,f. 11-13. 

 1872. 

 Red Willow Lake. 



Order HORMOGONEAE 



Fam. Oscillatoriaceae 



Genus oscillatorta Vauch. 



Oscillatoria amphibia Ag. 



Mission Bay, Devils Lake; East Lake. 



Also recorded by Snow (1902) from the plankton of Lake Erie. 

 O. brevis (Kiitz.) Gomont. 



Wheeler's Pond, I; East Lake; mouth of Minnewaukon Bay, 

 Devils Lake, below grade. 



O. chalybea Mertens. 



Mission Bay, Devils Lake; Mission Lake; Odessa, I; mouth of 

 Minnewaukon Bay, Devils Lake, below grade. 



O. janthiphora Fiorini-Mazzanti in Gom. Mon. Osc. p. 253. 

 pi 7, /. 18, 20, 81. 1893. PI. 21, fig. 10. 



Mission Bay, Devils Lake; Mission Lake; East Lake; mouth 

 of Minnewaukon Bay, Devils Lake, below grade; inlet of Lake A. 



