124 



CYMBELLE.E. 



SUB-FAMILY I. RAPHIDIE.E. 



Frustules mostly bacillar in valve view, sometimes broadly 

 oval, always with a distinct raphe and nodules on one or both 

 valves. Central nodule rarely absent or obscure ; valves 

 simple or complex. Raphe generally prominent in valve 

 view, occasionally in girdle view, especially when constricted, 

 w T ith nodules at the constrictions. Frustules always without 

 teeth, spines, awns, or processes. 



ANALYSIS OF TRIBES. 



Valves alike 



Valves unlike 



f Valves more or less arcuate or cymbiform, not symmetri- 

 cally divided by the raphe .... 



f Valves symmetrical ; central nodule 

 either equally distant from ends 

 or absent, or rudimentary or 

 divided .... 



Valves symmetri- 

 cally divided 

 by the raphe . 



I 



r Valves cuneate 



Valves 

 cuneate 



n o t 



| Valves asymmetrical with apices of 

 L unequal breadth (valves cuneate) 



Frustules genuflexed, nodule or 

 stauros on one valve only, usually 

 on the conca/e margin (at the 

 constriction) valves rarely broadly 

 oval .... 



Frustules with a central nodule on 

 only one valve, valves generally 

 broadly oval, rarely bent, never 

 genuflexed 



Cymbelleee. 



Naviculeae. 



Gomphonemese. 

 Gomphonemeee. 



Achnantheae. 



Cocconideae. 



Tribe i. Cymbelle/E. 



Connecting membrane highly developed on the dorsal 

 side, so that the two valves are seen at the same time 

 and nearly flat ; central nodule very apparent, rounded 

 or changed into a stauros, raphe without keel . 



Frustules with 

 connecting 

 membrane very 

 broad, often \ Frustule constricted as Amphora, but the raphe furnished 



longitudinally 

 plicate, striate, 

 or punctate 



I 



with a keel 



Valve very asymmetrical, with dorsal and ventral parts 

 situated in different planes and the raphe elevated on 

 a very projecting keel .... 



Amphora. 

 Amphoropsis. 



Auricula. 



Frustules with f 

 connecting 

 membrane nar- ,, , 

 row and neither \ , , 

 longitudinally 

 punctate nor 

 plicate . . t 



without 



f Frustules free or stipitate ; terminal 

 nodules near the apices, raphe 

 more or less arcuate 



Frustules often enclosed in tubes ; 

 terminal nodules very distant 

 from apices ; raphe quite straight 



Cymbella. 



Encyonema. 



