164 



NAVICULA. 



Valves not 

 1 inear. 



c. Valves having one or more narrow marginal or sub-marginal sulci. 



( Valves lanceolate, large ; striae radiate, fine, leaving a large 



blank space round the centre nodule . . .16. Formosa?. 



Valves elongate, generally more or less tri-undulate ; sulcus 

 marginal often inconspicuous ; raphe surrounded by a 

 hyaline space lanceolate, narrow ; striae radiate . . 17. Limosse. 



Striae sub-parallel, often slightly oblique in reference to the 

 longitudinal axis of the valve ; sulcus broad, very 

 L conspicuous . . . . . . .18. Affines. 



Valves linear ; striae fine, sub-parallel ; sulcus very conspicuous ; terminal 

 (, nodules elongate, distorted . . . . . . .10. Lineares. 



d. Valves more or less linear, without any sulcus. 



Striae radiate, occupying only the margin of the valves 



Striae generally bent, reaching the raphe ; valves with smooth, thickened 



. 20. Americana?. 



apices ....... 



Very small navicular with hardly visible structure. 



. 21. Bacillese. 

 22. Minutissimse. 



I. Pinnulariae. 



a. Striatum not interrupted by a marginal sulcus. 

 * Majores. -Valves regularly elliptic-linear, often slightly inflated at the 

 median portion and at the apices. Size usually large ; costae usually broad 

 and robust. 



ANALYSIS OF SPECIES. 



Costae very distant from raphe ; size very con- 

 siderable . . . N. nobilis. 



Costae f 

 rather 



approxi- 

 mate to \ 

 raphe ; 

 size 



medium. [_ 



Valve showinsr a hvaline band in the form of a false stauros . N. cardinalis. 



Valve inflated at the median portion . N. major. 

 Valve not inflated at the median 



portion 



N. viridis. 



f Raphe bent like a brace, showing in girdle view- 

 longitudinal hyaline spaces . . N. Trevelyana. 



I 



Valve showing a 

 false stauros. 



Raphe straight in the middle of the valve ; girdle 

 face without hyaline spaces 



N. 1 ectangnlata. 



f Striae very oblique, reaching ihe 



raphe everywhere . . . N. cruciformis. 



I 



Striae parallel, perpendicular to the 



raphe 



. N. quadratarea. 



N. nobilis Ehr. (Abh. 1840, p. 20, H.v.H Atl., pi. 5, f. 2* ; 

 Type No. 52), plate 2, fig. 67. 



Valve linear-elliptic, inflated in the median portion and at the apices with 

 coarse costae, considerably distant from the raphe. Girdle face linear with 

 rounded angles. Costae radiate, very robust, 5 or 6 in 1 c.d.m. Length, 

 20 to 40 c.d.m. 



Fresh water. Antwerp; probably not very rare. England, etc. 



