THE FRESH-WATER ALGAE 



131 



45 (46) Valves showing a wave-like margin in girdle view. 



Cymatopleura W. Smith. 



This is a large diatom which is 

 easily recognized by the undulat- 

 ing outline of the girdle side. 



The genus is rather small, and 

 WoUe reports but seven species. 



Fig. 93. Cymatopleura apiculata 

 W. Smith, a. Valve side. b. girdle 

 side. X 600. (Original.) 



46 (45) Girdle view without wave-like margins Surirella Turpin. 





UUOUUL'uuuUua 



QQoaaninmaa 



This genus is widely distributed 

 ■4 and of frequent occurrence in all re- 

 gions where diatoms are found. Some 

 species are very large and conspicu- 

 ous, especially in the plankton. 



Fig. 94. Surirella sp. Smith. a. 

 Valve side. b. girdle side. X 585- 



(Original.) 



47 (42) Valves without keels. . 4^ 



48 (59) Cells without deep inner partitions sometimes with imperfect septa. 49 



49 



(55) Valves with transverse costae So 



qo (';4) Valves symmetrical with reference to a transverse axis. 



Family Diatomaceae . . 51 



Cells symmetrical with reference to both axes, borne in long chains; transverse striations 

 distinct and uninterrupted except in some cases by a longitudmal plain band. 



51 (52, 53) Valve side oval or linear, transverse markings uninterrupted, 

 girdle side rectangular, cells mostly in zig-zag chams. some- 

 times in short filament Z)/(2/c7wa de Candolle. 



^^^^^<^^^P^aj 



Fig. 9 V DiaUma elongaium Agardh. a. Valve 

 ^ side. b. girdle side. X about 300. (After W. 

 Smith.) 





