62 WISCONSIN PHYTOPLANKTON 



plane. Cell wall with a transverse to arcuate row of irregularly 

 disposed subapical pores. (Facultative planktont.) 



Cells 52-63 /x long- with spines, 48-57 /x long without spines ; 

 75-95 IX broad with spines, 48-53 [x broad without spines ; isthmus 

 12.5-15 [x broad; spines 10-20 ;u, long. 



Beaverdam (s), Lindy (I'rr), Sand (rr), Silver (rrr). 



The chief character of this variety, Avhich Johnson erroneously 

 referred to X. antilopaeum var. javanicum Nordstedt, is the rather 

 irregular row of subapical pores. W. & G. S. West have considered 

 this a variety of X. hastiferum Turner but as the accessory apical 

 processes are of quite rare occurrence I feel that the variety belongs 

 rather to X. su})hastiferum. The peculiar cell shown in Figure 7 

 was found in the plankton of Beaverdam lake. 



STAURASTRUM Meyen 1829. 



Cells variable in size, with the length (without processes, spines 

 or other appendages) generally somewhat greater than the breadth, 

 median constriction usually deep though at times scarcely dis- 

 cernible, sinus generally acute-angled and isthmus narrow ; semi- 

 cells cylindrical, spherical, ellipsoidal, triangular, campanulate, 

 cyathiform, hexagonal or variously shaped; with the cell wall 

 smooth or punctate, without ornamentation or bearing granules, 

 mucros, denticulations, simple to emarginate verrucae, spines, or 

 combinations of these ornamentations; angles of a majority of the 

 species continued in processes of variable length, though usually 

 long, that in turn almost always have some sort of ornamentation 

 and usually terminate in a truncate end with short divergent spines, 

 at times with bifurcate ends that resemble spines ; processes ordi- 

 narily arising in one whorl though sometimes in two transverse 

 series of whorls. Vertical view at times Avith a bilateral symmetry 

 though commonly with a radial symmetry; radially symmetrical 

 species with triangular forms predominating though the 4-8 angled 

 or radiate species not uncommon and with the number of angles as 

 high as eleven in one whorl. Chloroplast generally with a simple 

 axial mass containing one pyrenoid and with deeply incised lobes 

 of variable size running to each angle of the cell, at times, especially 

 in the larger species, with several pyrenoids in each lobe and with 

 various irregularities; in very rare instances with parietal chloro- 

 plasts. Cells, particularly the plankton species, at times enclosed 

 in a spherical gelatinous envelope. 



Zygospores infrequently angular, usually spherical and with nu- 

 merous conical elevations that are continued in long spines that have 

 simple or furcate apices. 



The genus comprises so many species of such variable shape that 

 it is exceedingly difficult to describe it in anything but the most 

 general terms. In spite of the groups of species which at first 

 glance appear to have little in common with one another there are 

 so many transition forms that it is impossible to break it up into a 



