Ophiocytium majus Naegeli 1849, p. 89 

 PI. 94, Figs. 17, 18 



Cells free-floating, cylindrical, relatively long; S-curved, spiral, 

 or lunate; one end truncate, the other with a short, sharp spine 

 bearing a spherical enlargement at its tip; 7.8— 17/x in diameter, 

 152/i, long. 



Rare; in bogs and in tychoplankton of lakes. Mich., Wis. 



Ophiocytium mucronatum (A. Braun) Rabenhorst 1868, p. 68 



PL 94, Fig. 16 



Cells irregularly cylindrical, curved, attached by a short stipe and 

 a hemispherical disc to filamentous algae; apical region slightly 

 swollen, terminating in a slender spine; older individuals with cells 

 of the second generation attached at the anterior end; diameter 4-7 ju; 

 46-48/i, long. 



Tychoplanktonic in lakes and swamps. Mich., Wis. 



Ophiocytium parvulum (Perty) A. Braun 1855, p. 55 



PL 94, Fig. 20; PL 96, Figs. 4, 5 



Cells free-floating, cylindrical, long and strongly S-curved or spiral, 

 truncate at both ends, S-lO^a in diameter. 



Common in the tychoplankton of many lakes. Mich., Wis. 



ORDER HETEROTRICHALES 



This well-defined order is composed of the strictly filamentous 

 forms in the Xanthophyceae. In one of the suborders, Tribonematales 

 (Pascher 1937-1939), the filaments are unbranched, whereas in a 

 second suborder ( Heterocloniales ) , they are simply branched. 

 Although most forms are free-floating, some are attached, at least 

 when young, by a basal stipe and adhesive disc. The duplex mor- 

 phology of the wall is apparent in some genera in the vegetative 

 condition, but in others it is evident only when the cells separate to 

 liberate zoospores or aplanospores. Chromatophores are parietal 

 plates or discs, often faintly pigmented. Reproduction is by zoo- 

 spores, aplanospores, and in some genera by isogametes, the motile 

 cells bearing 2 flagella of unequal length. Only one family is repre- 

 sented in our region, the Tribonemataceae. Pascher ( I.e. ) separates 

 Tribonema from other genera, however, on the basis of wall structure 

 details, recognizing the Tribonemataceae and the Heterotrichaceae 

 to which Bumilleria is assigned. According to some views this 

 separation is not justified. 



[365] 



