1923] 



MOORE AND CARTER — ALGAE FROM NORTH DAKOTA LAKES 411 



It is somewhat doubtful, however, whether this desmid 

 should be placed as a form of St. Manfeldtii, which, with its 

 short, stout processes, presents a somewhat different appearance 

 to the alga under consideration, which has long graceful proc- 

 esses. By reason of this latter character it should probably be 

 placed as a form of St. gracile. 



St. paradoxum Meyen, var. evolutum West, Brit. Desm. 5: 

 107. pi. 145, f. 7-8. 1923 ( = St. tetracerum Ralfs var. evolutum 

 West in Proc. Bot. Soc. Edinburgh 23: 27. pi. 2, f. 31. 1905). 



Forma biradiata PI. 21, fig. 4. 



Length, without processes, 7 \i, including processes, about 37 

 n; breadth, without processes, 5 \i, including processes, 40 t*; 

 breadth of isthmus 3.5 (i. 



Strawberry Lake; Red Willow Lake. 



This species bears some resemblance to St. tetracerum Ralfs 

 and is somewhat similar to St. tetracerum var. subexcavatum 

 Gronblad in Act. Soc. Fauna Flora Fenn. 49: 62. pi. 5, f. 28, 29. 

 1921, which has processes considerably longer than the typical 

 form. The North Dakota specimens, however, have still longer 

 processes in comparison with the very minute body of the cell. 

 The long slender processes suggest at once St. subgracillimum 

 West in Trans. Linn. Soc. II. 5: 263, pi. 17, f. 3, 4. 1896, but the 

 form of the body is different, and the strong divergence of the 

 processes precludes any relationship to that species. It is most 

 likely that the alga should really be considered a biradiate form 

 of St. paradoxum var. evolutum, which was described by the 

 Wests from the plankton of lakes in the Shetland Islands. The 



cells were usually twisted at the isthmus, and there was a slight 

 variation in the comparative length of the processes. The 

 dimensions are only slightly smaller than those given by West. 



Family Ztgnemaceae 



Genus zygnema Ag. 



Sterile species of Zygnema were present in samples taken from 

 Gordon Lake and Long Lake. 



