HOW TO KNOW THE FRESH-WATER ALGAE 

 130b Cells themselves fusiform; without such a sheath 131 



131a Setae formed by a narrowing of the cell to a fine point; chloro- 

 plast laminate (plate-like), not extending the full length of the cell. 

 See Fig. 89 OUROCOCCUS 



131b Setae formed by a fine spine on the wall, extending from the 

 narrowed tips of the cells. See Fig. 88 SCHROEDERIA 



132a (129) Cells many (20 or more) times longer than wide; the chloro- 

 plast with a row of pyrenoids. Fig. 98 CLOSTERIOPS1S 



Figure 98 



Fig. 98. Closteriopsis longissima Lemm. 



There is but one species reported from this country. Although it 

 superficially resembles a Closterium (Fig. 86) it is easily separated on 

 the basis of the single, plate-like chloroplast which may be notched or 

 crenulate along the margin. At times the cells are slightly curved but 

 usually are more nearly straight than any of the species of Closterium. 



132b Cells less than 20 times the diameter long; slender needles or 

 narrowly fusiform cells with one pyrenoid sometimes evident. 

 See Fig. 68 ANK1STRODESMUS 



133a (127) With a notch in the ends of the cell. Fig. 99 



, TETMEMORUS 



Fig. 99. Tetmemorus laevis (Kuetz.) Ralfs. 



This is a genus belonging to the true 

 desmids, having a wall in 2 pieces that 

 adjoin in the midregion. Species that 

 Figure 99 are found in this country seem to be con- 



fined to highly acid situations. There are several species reported, 

 some with cylindrical shapes and some with the ends tapering, but 

 always with a prominent polar notch. A placoderm desmid. 



69 



