1923] 



MOORE AND CARTER — ALGAE FROM NORTH DAKOTA LAKES 405 



occurrence of heterocysts. Spores were also very rare, and being 

 immature, were considerably smaller than the dimensions given 

 by Klebahn, although in general form they were very similar to 

 Klebahn's figure. West (Linn. Soc. Bot. Jour. 38: 170. pi. 9, f. 

 8. 1907) records a similar rigid but sterile form of Anabaena from 

 t he plankton of Lake Tanganyika which differs only in the some- 

 what greater diameter of the trichomes, and the smaller propor- 

 tionate size of the heterocysts. 



A. spiroides Klebahn in Flora 80: 268. pi 4, /• 11-13. 1895. 



PI. 21, figs. 11, 12. 



Mission Bay, Devils Lake; Mission Lake. 



Diam. trich. 8 (x; diam. spor. 11-13 (x. 



The specimens were almost exactly similar to Klebahn's ex- 

 amples, the only difference being in the slightly smaller size of 

 the spirals, which were about 30-40 [i in diameter, and the turns 

 30-40 p. apart, instead of 45-54 ^ in the first case and 40-50 n 

 in the second as given by Klebahn. Spores were very abundant, 

 and only very slightly longer than broad. The typical form has 

 previously been known only from continental Europe, although 

 var. crassa Lemm. has been recorded from the Wisconsin lakes 

 and from Massachusetts. 



Genus aphanizomenon Marr. 



Aphanizomenon flos-aquae (L.) Ralfs. 



General in most of the plankton samples, often pure and in 

 abundance as a "water-bloom." 

 Wheeler's Pond, I; Crow Lake; Fish Lake; Coe Lake; Painted 



Woods Lake; Sweetwater Lake; Jim Lake. 



Family Rivulariaceae 



Genus calothrix Ag. 



Calothrix fusca (Kutz.) Born, et Flah. 



Crow Lake: growing in the gelatinous colonies of Chaetophora 

 elegans; Devils Lake, amongst Ruppia near Station. 



C. scytonemicola Tilden, Minn. Alg. p. 265. pi. 17, f. 7. 1910. 

 Dion Lake: growing in clusters on Cladophora sp. 



