410 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



Genus arthrodesmus Ehr. 



Arthrodesmus controversus W. & G. S. West in Brit. Desm. 4: 

 pi 115, f. 12-14. 1911. 



Cut-off Pond, Stump Lake. 



This minute desmid occurred in several samples and the regular 

 splitting of the cells at the isthmus left no doubt as to its desmid 

 character. Borge (in Arkiv f. Bot. 15: 40. pi. 8, f. 21. 1918) has 

 described a var. brasiliense from Brazil. The typical form has 

 only previously been known from Europe. 



Genus staurastrum Meyen 



Staurastrum gracile Ralfs. 



Length, without processes, 17 n, including processes, 17-18 n; 

 breadth, without processes, 8 n, including processes, 33-36 n; 

 breadth of isthmus 4 n. 



Strawberry Lake; Carpenter Lake. 



The specimens were very small, but exactly typical in form. 



St. gracile Ralfs forma. PL 21, fig. 3. 



Length, without processes, 37-42 n, including processes, about 

 62 \i; breadth, without processes, 18-24 p, including processes, 

 79-89 \i; breadth of isthmus 10-17 n. 



Strawberry Lake; Carpenter Lake; Red Willow Lake; North 

 Twin Lake, near Wing. 



This species is almost exactly identical with a certain form 

 described by Dr. J. LutkemGller as St. Manfeldtii Delp. var. 

 gracile Liitk. from the plankton of a lake in Austria. This form 

 was never published but appears under this name in a letter 

 from Dr. Ltitkemuller to the late Professor G. S. West, dated 

 June, 1911. The dimensions of Liitkemuller's form are: length, 

 without processes, 30 n, including processes, 58 \i ; breadth, with- 

 out processes, 20 \l, including processes, 70 (x; breadth of isthmus 

 7.3 |x. The Austrian and the North Dakota forms are very similar. 

 In both the processes are slightly divergent and the body of the 

 semicell is cup-shaped. The chief difference lies in the some- 

 what deeper constriction and the stronger denticulations of the 

 Austrian form, and the presence near the isthmus of a few 

 granules beneath each process, not evident in the North Dakota 

 specimens. 



