the test cavity; wall smooth or lightly punctate, golden- or reddish- 

 brown; test 23/A in diameter, 23-26;u long. 

 Tychoplankter; in swamps. Wis. 



Trachelomonas volvocina Ehrenberg 

 1833, pp. 315, 331; 1838, p. 48 

 PI. 83, Figs. 1, 7, 8 

 Test globose; flagellum aperture without a collar; wall yellowish, 

 sometimes colorless, smooth; test 16-20/* in diameter. 



Generally distributed; common in ponds and ditches. Mich., Wis. 



Trachelomonas volvocina var. compressa 

 Drezepolski 1925, p. 224 

 PL 83, Figs. 2, 3 

 Test depressed-globose or spheroidal; flagellum aperture sur- 

 rounded by a thickening of the wall, which is yellow and smooth; 

 test 18.5/t in diameter, 20.3/* long. 

 Tychoplankter; in swamps. Wis. 



Trachelomonas volvocina var. punctata Playfair 1916, p. 9 



PI. 83, Fig. 12 

 Test with a distinctly punctate wall, 10/* in diameter, 20/* long; 

 otherwise similar to the typical. 

 Tychoplankter; in swamps. Wis. 



COLACIUM Ehrenberg 1832b, p. 115 



Cells losing their flagellum and becoming attached by a stalk-like 

 extension of the membrane, with the anterior end downward, to 

 small animals (Crustacea, etc.); chloroplasts many ovoid discs, 

 with or without a pyrenoid; pigment-spot usually evident in the 

 lower (apical) end; cells solitary or in arbuscular colonies. 



Key to the Species 



Cells in plume-like colonies, stalks as long 



as or longer than the cells - C. arbuscula 



Cells solitary, or 2-4 on short, thick stalks C. vesiculosum 



Cohcium arbuscula Stein 1878, III, p. 1 

 PL 89, Fig. 22 

 Cells elliptic or fusiform, joined by a branched, gelatinous stalk 

 to form plume-like, arbuscular colonies; chloroplasts many ovoid 



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