4. Thallus euplanktonic (or incidentally tychoplanktonic ) spherical or 

 elongate, composed of relatively few cells evenly distributed or 

 arranged in groups of 4 within the colonial mucilage T. lacustris 



4. Thallus not planktonic, although frequently becoming free-floating 

 in age; at first tubular and sac-like, later expanded and laciniate, 

 forming skeins T. lubrica 



Tetraspora cylindrica ( Wahl. ) C. A. Agardh 1824, p. 188 



PI. 5, Figs. 1, 2 

 Thallus an attached, irregularly lobed cylinder of firm mucilage 

 which may be 1 meter long, narrowed at the point of anchorage. 

 Cells scattered, showing arrangement in 4's only when young, 

 14-17/x in diameter. 



Forming long, green, intestiniform strands in streams of cold 

 water. Mich., Wis. 



Tetraspora gelatinosa (Vauch. ) Desvaux 1818, p. 18 

 PI. 5, Figs. 3, 4 



Thallus at first an attached cylindrical sac, later becoming bullate 

 and lobed but not perforate. Cells irregularly arranged in old plants 

 and differing in size, 2.5-13/x in diameter. 



The globular and bullate form of the thallus, even when old, is 

 the chief differentiating character of this species. It is impossible to 

 separate this species clearly from young plants of T. lubrica. 



In the quiet backwaters of lakes, among rushes. Mich., Wis. 



Tetraspora lacustris Lemmermann 1898d, p. 152 

 PI. 5, Fig. 11 



Thallus a free-floating, spherical, or elongate and irregularly 

 shaped, microscopic gelatinous colony containing relatively few 

 spherical cells, the long pseudocilia usually clearly evident. Cells 

 arranged in groups of 2 or 4; 7-10/a in diameter. 



This species is microscopic and apparently free-floating at all 

 stages. It should be compared with Sphaerocystis Schroeteri, from 

 which it may be differentiated by applying some simple stain to 

 determine the presence of pseudocilia. See Smith (1933, p. 352). 



Common in the plankton of several lakes and inlets. Wis. 



Tetraspora lamellosa Prescott 1944, p. 348 

 PI. 5, Fig. 6 

 Thallus irregularly lobed and saccate, free-floating. Cells spherical, 

 in 2's, with thick walls and gelatinous, lamellate sheaths which are 



[88] 



