i 3 6 



FRESH-WATER BIOLOGY 



15 (14) Cells not cask-shaped, with a narrow, shallow, central constriction; 

 end view elliptical or triangular, ends tapering or round. 



Spondylosium Archer. 



Cells 10 to 12 n broad: 8 to QH long, cells tapering towards 

 the ends. Membrane smooth or with slight prominences. 

 A pyrenoid in each cell-half, about which radiate from 4 to 6 

 chlorophyll plates. 



The cells of the filaments are united by the close adher- 

 ence of the apices of the cells. The filaments are frequently 

 twisted and enveloped in mucus. 



FIG. 112. 



Spondylosium papillatum W. and G. West. 

 (Original.) 



X6oo. 



1 6 (13) Cells deeply constricted in the middle 17 



17 (18) Cell-halves acutely pointed or oval; upper and lower surface of each 

 end furnished with a spine which meets a similar one on the 

 adjoining cell; end view fusiform. . . Onychonema Wallich. 



Narrow spines frequently present. In each cell-half a single axial 

 chroma tophore, composed of radiating plates about a central pyrenoid. 



Onychonema occurs in swamps and ponds but is not of very fre- 

 quent occurrence in America. 



FIG. 113. Onychonema loeve Nordstedt. X 600. (Original.) 



18 (17) Cell-halves oval in outline, with a deep central constriction; cells 

 united into filaments by small tubercles. 



Sphaerozosma Archer. 



Cells 22 to 33 M broad and about half as long, end view elliptical; 

 membrane smooth or with tiny warts near the ends of the cells. 



Sphaerozosma is distinguished from Spondylosium by the cells 

 being united by tubercles instead of by their apices directly. 



S. pulchrum var. inflatum Wolle is reported by Wolle as occur- 

 ring in such quantities as to color the water green. 



FIG. 114. Sphaerozosma vertebratum Ralfs. X about 300. (After de Bary.) 



19 (12) End view of cells triangular or quadrangular, seldom oval. 



20 



20 (21) No space at the center between the transverse septa; cells slightly 

 and narrowly constricted Desmidium Agardh. 



Filaments long, twisted. Cells flat at the 

 ends, | to $ as long as broad, so constricted 

 at the center as to give a scalloped lateral 

 outline to each cell. End view with as many 

 pyrenoids as there are angles, from each of 

 which radiate two chlorophyll plates. 



FIG. 115. Desmidium schwarlzii Agardh. a. side 

 view. b. end view. X 550. (Original.) 



