i 68 



NAVICULA. 



**Minores. Frustules of medium or small size, with valves of 

 variable form, rarely regularly linear, often inflated at the median 

 portion and diminuate at the apices ; costae medium or narrow. 



I. Terminal nodules not laterally dilated like a hook. 



a. Valves neither undulate nor constricted in the middle. 



ANALYSIS OF SPECIES. 



r 



Costa; 

 very 

 robust 

 and 

 very 

 dis- 

 tant. 



With- 

 out 

 any 

 false 

 stauros. 



f Costas 



dis- Valve sublinear, abruptly inflated in the 



tant i middle . . . . . N. 



j from j 



the Valve broadly lanceolate . . . N. 



I raphe. l_ 



lata, 

 alpina. 



Costas reaching nearly to the raphe, valve sublinear . N. borealis. 



Costa: 



ap- 

 proxi- 

 mate. 



With a 



false 

 stauros. 



Costas 

 ap- 

 proxi- 

 mate to 

 raphe 

 not per- 

 ceptibly 

 short- 

 ened 

 towards 



the 

 central 

 nodule. 



I 



f Valve very large, with obtuse apices, costas not 



resolvable . . . . . . N. divergens. 



Valve very small, apices acute, costas resolvable with N. costulata.* 

 L difficulty ...... 



f Valve r 



with- Valve slightly inflated at the median por- 



out a tion ; costs; very fine ; fresh water 



staur- ! species . . . . . N. sublinearis. 



onei- '[ 



form Valve linear, not inflated, costa; rather 



blank robust ; marine species . . . N. retusa. 



space. l_ 



Valve with stauroneiform blank space, apices 



rostrate-capitate . . . . . N. Hilseana. 



Costas 

 often 

 approxi- 

 mate to 



the 

 raphe, 

 and im- 

 per- 

 ceptibly 

 short- 

 ened 

 towards 



the 

 central 

 nodule. 



Valves 



in- 

 flated 

 at the 

 me- 

 dian 

 por- 

 tion 

 only 

 slight- 

 ly or 

 not at 

 all. 



Apices somewhat diminuate . N. Brebissonii. 



f Valves scarcely in- 

 flated in the middle N. stauroptera. 



Apices 

 not 

 ros- 

 trate 

 capi- 

 tate. 



Apices 



in- 

 flated. 



Valves 

 con- 

 sider- 

 ably 

 in- 

 flated 

 at the 

 me- 

 dian 

 por- 

 tion. 



Median in- 

 fl a t i o n 

 abruptly 

 diminuate 



Media n 

 i nflation 

 diminish- 

 in g im- 

 percep- 

 tibly up 

 to' the 

 apices 



N. Tabelleria. 



Apices 

 more 



or less 

 ros- 



trate- 

 capi- 

 tate. 



Valve exactly linear ; apices 

 strongly rostrate-capitate ; no 

 pseudo stauros 



Valve somewhat inflated with 

 subcapitate apices ; costas 

 rather distant ; a false stauros 



Valve somewhat inflated, apices 

 subcapitate ; costas approxi- 

 mate ; a false stauros. 



Valves 

 con- 

 sider- 

 ably 

 in- 

 flated 

 at the 

 me- 

 dian 

 por- 

 tion. 



Valve linear-oblong, with apices broadly 

 rostrate-capitate . 



N. gibba. 



N. bicapitata. 

 N. subcapitata. 

 N. appendiculata. 



N. globiceps. 



Valve linear-lanceolate, with apices to an 

 average extent rostrate-capitate . . N. Braunii. 



