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 o£ a typical Namctua. 



^^,,<jg=T , y> I I / / ^?g:~^ to one strongly arched, and they have sometimes been styled 



(^^SwN\vv\'///y/^I^^^7^ as asymmetrical Naviculas. Some authors include the genus 



^^^/777 ////i ii \\\\\\\''^y^^ ^ Coccotiema under Cymbella, but the name Cocconema is the 



^4////// l\\\\\^^^^ oldername and should be retained. WoUe reports 25 species 



^H44^//|\\\^;=^ of Cymbella. 



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



30 (29, 31) Cells much as in Cymbella, but usually larger and borne on 



gelatinous stalks Cocconema Ehrenberg. 



Fig. 84. Cocconema lanceolatum Ehren- 

 berg. X 375. (After West.) 



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

 hving in gelatinous tubes Encyonema Kutzing. 



Fig. 85. Encyonema attenvaldii Rabenhorst. X 250. 

 (After Wolle.) 



32 (12, 36) Girdle view as)ntnmetrical 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 nodtde 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 curvala Grunow. a. Valve side; b. girdle side. X380. 

 (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 CoccoNEmACEAE. 



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.) 



