THE FRESH-WATER ALGAE 



129 



29 (30, 31) Raphe straight or bent, ending in the middle of the valve ends. 



Cells free Cymbella Agardh. 



Cymbella varies in shape from that of a typical Nawcula 

 to one strongly arched, and they have sometimes been styled 

 as asymmetrical Navicidas. Some authors include the genus 

 Cocconema under Cymbella, but the name Cocconema is the 

 older name and should be retained. Wolle reports 25 species 

 of Cymbella. 



FIG. 83. Cymbella cuspidata Kutzing. X 600. (Original.) 



3 ( 2 9> 3 1 ) Cells much as in Cymbella, but usually larger and borne on 

 gelatinous stalks Cocconema Ehrenberg. 



FIG. 84. Cocconema lanceolatum Ehren- 

 berg. X375- (After West.) 



31 (29, 30) Raphe straight, not ending in the middle of valve ends. Cells 

 living in gelatinous tubes Encyonema Kutzing. 



FIG. 85. Encyonema auerwaldii Rabenhorst. 

 (After Wolle.) 



32 (i 2, 36) Girdle view asymmetrical with reference to a transverse axis, 

 the outline being wedge-shaped. 



Family GOMPHONEMACEAE . . 33 

 33(35) Girdle side straight. Gomphonema Agardh. 



FIG. 86. Gomphonema acuminatum Ehrenberg. a. Valve side; 

 b. girdle side. X 600. (Original.) 



34(11,38) A middle nodule and a raphe present on but one valve. . . 35 



35 (33) Girdle side curved; otherwise similar to Gomphonema. 



Rhoicosphenia Grunow. 



The two valves are unlike in shape and in the fact that the lower valve 

 possesses a raphe, a central and end nodules, while the upper valve possesses 

 only a pseudo-raphe and is without nodules. 



FIG. 87. Rhoicosphenia curvata Grunow. a. Valve side; b. girdle side. X 380. 



(After Schonfeldt.) 

 A B 



36 (32, 37) Girdle view symmetrical with reference to a transverse, but not 



to a longitudinal axis, the cells being arcuate and attached 



to higher algae Family COCCONEIDACEAE. 



Only one genus known Cocconeis Ehrenberg. 



Valves oval or elliptical, symmetrical with reference to both axes; raphe 

 straight, with middle nodules but without end nodules. Markings of faint 

 longitudinal punctate lines; girdle and end views both curved. 



FIG. 88. Cocconeis pediculus Ehrenberg. X 600. (Original.) 



