1923] 



MOORE AND CARTER — ALGAE FROM NORTH DAKOTA LAKES 399 



Genus microcystis Ktitz. 



Microcystis incerta Lemm. 

 Lake P. 



M. pulvera (Wood) Migula. 



Plankton of Lake Metigosche; plankton of Jarves Lake; 

 plankton of Strawberry Lake; plankton of Ensign Lake. 



M. stagnalis Lemm. in Arkiv f. Bot. 2 s : 146. 1904 (Polycystia 

 stagnalis Lemm. in Ber. d. deut. bot. Ges. 18: 24. 1900; Polycystic 

 pallida Lemm. in Bot. Centralbl. 76: 154. 1898). 



Previously known only from Europe. 



Strawberry Lake. 



Genus clathrocystis Henfrey 



Clathrocystis aeruginosa (Kiitz.) Henfrey. 



General and usually very abundant in the plankton of Wheeler's 



Pond, I, Stump Lake; Lake Metigosche; Jarves Lake; Straw- 

 berry Lake; Carpenter Lake, Fish Lake; Gravel Lake; Gordon 

 Lake ; Blue Lake ; Juanita Lake ; Long Lake, near Binf ord ; Long 

 Lake, near Ruso; Crooked Lake; Brush Lake; Florence Lake; 

 Wood Lake; Spirit wood Lake, I; Jim Lake; North Twin Lake, 

 near Wing; Lake Williams; Spiritwood Lake, II; South Wash- 

 ington Lake; Ensign Lake; Lake Y or South Twin Lake, near 

 Robinson; Dion Lake. 

 Var. major (Wittr.) G. M. Smith. 



Frequent with the typical form in the plankton of Ensign Lake; 

 Carpenter Lake. 



C. holsatica Lemm. in Plon. Ber. 10: 150. 1903; Forti in DeToni, 

 Syll. Atg. 5:95. 1907. 



Plankton of Spiritwood Lake, II, near Jamestown. 



Figures of the typical form of this species were not available. 

 Comparison was made, however, with Lemmermann's figure of 

 var. minor in Abh. Nat. Ver. Brem. 18: pi. 11, f. 1. 1906, and 

 the general appearance was very similar. In the size of the cells, 

 however, and in the thick transparent gelatinous sheath of the 

 colony, the North Dakota specimens agreed better with the 

 description of the typical form. C. holsatica has only previously 

 been known from Germany, and its variety from Siam. 



