ij6 



NAVICULA. 



b. STRLE VERY DISTANT AND VERY ROBUST ; VERY SMALL FORMS WITH 

 TERMINAL NODULES LIKE HOOKS. 



r Valve rhomboidal with acute apices ; median portion furnished with a broad 



pseudo-stauros . . . . . . . . N. costulata. 



'] Apices capitate ; no pseudo-stauros . . . . . . N. humilis. 



[_ Valve elliptic ; with obtuse apices, median stria; simulating a schizo-stauros N. nana. 



II. Median striae radiate, terminal striae perpendicular to the raphe (straight). 



. N. cancellata. 

 , N. inflexa. 



f f Valves narrowly f Apices short, acute 



| Median striae of | linear or -J 



quite the -J linear-lanceolate. [_ Apices rather long, inflected 

 same length. 



i_ Valves broadly lanceolate, robust forms . . . N. fortis. 



Median strire | 

 alternately long -| 

 and short. 



( Valve rather narrowly lanceolate, with sub-obtuse apices ; 

 hyaline area not stauroneiform ; striae with 



very delicate puncta 



. N. digito-radiata 



Valve broadly lanceolate or elliptic, with very obtuse 

 apices; hyaline area stauroneiform; striae with 

 strong puncta .... 



N. Reinhardtii. 



III. All the striae radiate. 



Striae very 

 robust. 



Without any 



appearance 



of a false 



stauros. 



Valves 

 lanceolate. 



f Valve broadly lanceolate, 



striae very distant . N. 



> Valve very narrowly 

 lanceolate, striae 

 approximate . N. 



I 



Striae fine f Valve with obtuse apices N. 



approximate j 



10 to 12 in i j Valve with acute apices . N- 



c.d.m. L 



' Valve with apices broadly rostrate, not 



Showing the capitate . . . . N. 

 semblance 



of a false -J Valve with apices capitate . K. 

 stauros. 



Valve with apices rostrate-acute . . N. 



f Apices somewhat constricted . . . . N. 

 Valves 



oval-oblong, -j Apices diminuate, rostrate, not capitate . . . N. 



(_ Apices rostrate, sub capitate . . . . N. 



Valves with apices strongly rostrate, not capitate . . N- 



Valves 

 linear. 



distans. 



longa. 

 Solaris, 

 lanceolata. 



Gastrum. 



Anglica. 



crucifera. 



Semen, 

 cajitata. 

 dicephala. 

 apiculata. 



Valves neither rostrate nor capitate, but very gently inflated 



at the median portion, connecting zone very broad . N. Kiitzingiana. 



IV. All the striae perpendicular to the raphe. 



f Valve very long, narrow, lanceolate, striae 'very robust and very distant, 



girdle face narrow . . . . . . N. directa. 



j Valve short, rather narrowly lanceolate, striae fine, approximate, girdle face 



I 



equal to 3-4 times the breadth of the valves 



. N. Northumbrica. 



