>s v 









! L 



NAVICULA. 





i6- 



A. True Naviculse. Frustules free, not enclosed in gelatino- 



mucous fronds. 



Sub-genus I. Navicula. 



Analysis of Groups. 



I. Valves without distinct puncta, furnished with costae (canaliculi) or 

 robust strire, having the appearance of costae ; never didymous in form. 



True costre, not resolvable into beads . . . 1. Pinnularise. 



Striae robust, having the appearance of costae but resolvable into beads; 



strice radiate, almost or quite reaching to the raphe . . .2. Radiosse. 



II. Valves with very distinct puncta or fine striae having no semblance 

 to costae or with costae ; or again with costae alternating with rows of beads. 



a. Valves wit/i strne interrupted by two sulci near the raphe. 



{ ( Valves more or less constricted in the 



Sulci not j median portion 



Sulci straight. -| lvre - s haped. \ y a i ves without constriction in the median 



I portion .... 



I Sulci lyre-shaped ...... 



L Sulci very broad and occupying the greater portion of the valv^ 



b. Valves more or less lanceolate, or elliptic or linear lancvlate, without any sulcus. 



3. Didymse. 



4. Ellipticse. 



5. Lyratse. 



(J. Hennedyjse. 



f 



3 

 O 



cj 



'a, 

 in 

 c 

 o 



.2 



Valves having the appear- f Valves having the appearance of a 

 ance of a stauros, either | grater, with very large, elongated 



by the absence of striae or -{ beads .... 



by the space between j 

 them . . . t Valves with tine striae . 



Striae 

 leaving 



a con- 

 siderable 



hyaline 



Valves 

 without 



any 

 appear- 

 ance 

 of 

 stauros. 



Valves 

 with 



puncta 

 not 



forming 



longitu- 

 dinal 

 lines 

 in 



zig-zag. 



Striae 



with 

 beads not 

 forming 

 longitu- 

 dinal 

 lines. 



Striae 

 with 

 beads 

 forming 

 longitu- 

 dinal 

 and 

 trans- 

 verse 

 lines. 



Hyaline space very 

 elongate and in- 

 finitesimally di- 

 minuate . 



! 



space 



round 



the raphe 



and 



central 



nodule. 



Beads extending over the whole 

 valve .... 



Hyaline space 

 rounded and 

 abruptly diminu- 

 ate 



7. Asperse. 



8. Stauroneidese. 



9. Palpebrales. 



10. Abbreviate. 



11. Perstriatse. 



Valve very elongate, 

 linear . 



Valve lanceolate . 



almost 



12. 



13. 



Johnsoniese. 

 Crassinerves. 



Valves 

 with 



puncta 



forming 



longitu- 

 dinal 

 lines 

 in 



zig-zag. 



Striation almost invisible with the best objectives, valve linear lanceolate 

 ^ simulating an Amphipleura ....... 



Zig-zags interrupted by pale places where the 



valve is depressed . . . .14. Sculptese. 



Lines in zig-zag, regular, not interrupted . 15. Serian'eEe. 



\3bis. Fusiformes. 



