WISCONSIN PHYTOPLANKTON 99 



a great resemblance to the twisted forms of S. excavatum "W. & G. S. 

 West that G. S. West found in the Australian plankton. (Jour. Linn. 

 Soe. Bot. 39: 71, pi. 6, figs. 19-20. 1909) but cannot be placed in 

 8. excavatum since it lacks the characteristic apical excavation. The 

 body of the cell of S. contortum is much smaller and less sharply de- 

 fined than those of other biradiate species. 



36. Staurastrum Chaetoceras (Schroder) comb. nov. PI. 76, Figs. 



21-24; PI. 77, Fig. 1. 



staurastrum polymorphum Meyen (?) var. chaetoceras Schroder in Zacharias, 

 Forschungsbr. a. d. Biol. Stat, su Plon 6": 131, text figs. A-C. 1898. 



Cells fairly large, length (with processes) about equal to the 

 breadth, deeply constricted, sinus obtuse-angled and with a blunt 

 apex, isthmus narrow ; semicells obversely triangular, with the ventral 

 margins sublinear and the apex flattened; angles continued in long 

 divergent straight processes, the angle of divergence being a con- 

 tinuation of the angle of the sinus, processes slightly attenuated, 

 delicate, with transverse concentric rings of minute granules and 

 terminating in four minute teeth ; body of semicells with outline finely 

 crenulate and with a few scattered subapical granules, at times with 

 a transverse row of granules just above the isthmus. Vertical view 

 narrowly elliptic (very rarely triangular) with the poles continued 

 in straight processes whose ornamentation is as in the front view. 

 (Euplanktont.) 



Zygospores unknown. 



Cells 46-89 /x long with processes, 19-22 /x long without processes ; 

 breadth with processes 65-89 fi, without processes 16-22 ^ ; breadth 

 at isthmus 5.5-6.5 ju, ; thickness 10 [x. 



Bear (rrr). Big Butternut (rrr), Blake (ss). Bone (r). Camp (r), Center (r), 

 Chain (rrr). East (rr), Found (rr), Half Moon (r), Little Bass (s), Little 

 Butternut (rr), Lost (r), Big McKenzie (rrr), Middle McKenzie (rr), Pokegama 

 (ss), Whitefish (rrr), Wolf (rrr). 



In describing the alga Schroder placed it as a variety of ;S^. para- 

 doxum Meyen (by mistake written S. polymorphum Meyen) but I 

 feel that if it is to be given varietal rank it should be a variety of 

 8. tetracerum (Kiitzing) Kalfs. In spite of occasional triradiate 

 semicells it should be grouped with the biradiate species and sep- 

 arated from the other species of this type by the lack of verrucae at 

 the apex of the semicells. Most of the biradiate species also lack the 

 concentric rings of granules on the processes that are found in 

 8. Chaetoceras. These rings are easily overlooked, especially when 

 the cell contents are present. In certain stations forms with excep- 

 tionalty long processes were observed (Fig. 1). 



