Centritractus belanophorus Lemmermann 1900d, p. 274 

 PL 95, Figs. 37, 38 



Cells usually elongate-cylindric ( rarely elongate-ovoid to ellipsoid 

 when young), straight or slightly curved, with a long, slender spine 

 at each pole; junctures of the wall sections conspicuous, one showing 

 near each end of the cell; chromatophores 1 or 2 parietal plates; 

 pigment-spot sometimes apparent (especially in cells with but 1 

 chromatophore ) ; cells 8-12-(15)|U. in diameter, up to 40/x long; 

 spines about as long as the cell. 



In acid bog lakes. Mich., Wis. 



Centritractus dubius Printz 1914, p. 72 

 PL 93, Figs. 28, 29 

 Cells broadly ellipsoid or narrowly ovate to subcylindrical, the 

 poles broadly rounded and furnished with a stout, straight spine; 

 overlapping of the 2 wall sections very evident, the juncture near 

 the midregion of the cell; chromatophores 2-5 parietal plates or 

 folds; cells 5-7.8/t in diameter, 41.6/a long including spines, 10-14/x 

 long without spines. 



Rare in plankton of several soft water and acid lakes. Wis. 



FAMILY CHLOROTHECIACEAE 



This distinctive but small family includes free-floating or attached 

 cylindrical cells which have a thick, often lamellated wall (a char- 

 acter usually determinable only in stained preparations). The wall 

 is formed of 2 pieces decidedly different in size, the longer one of 

 which overlaps the other. In one genus (Ophiocytium) , the cells 

 elongate by a stretching of one of the pieces, and additional layers 

 of wall material are erected to foiTn a series of telescoping cups. 

 There may be a spine at one or both poles, or the apices may be 

 smooth. The cells are multinucleate, at least in age. Usually members 

 of this family are solitary, but in a few species colonies are formed 

 when successive generations of cells remain attached in tiers by the 

 in situ germination of zoospores in or on the old mother cell wall. 

 The plants are incapable of multiplication by cell division. (See 

 Pascher 1937-1939 for a treatment of the taxonomy of this family. ) 



Key to the Genera 



Cells attached by a broad, short stipe, or sessile; 



solitary; not growing by increase in length Chlorothecium 



Cells free-living or, if attached, furnished with a slender stipe; 

 cells elongate-cylindric and increasing in 

 length; often colony-forming Ophiocytium 



[361 1 



