NAVICULA. 



T 75 



B. Striation interrupted by a marginal sulcus. 



N. blanda Ad. Schm. (Nordsee, p. 90, pi. 2, f. 27*; Pinnularia 



Ergadensis Greg., T.M.S., 1856, p. 48, p. 5, f. 22 ?) plate 25, fig. 707. 



Valves linear, with parallel or subparallel costae, apices rounded, leaving a 

 considerable hyaline area round the central nodule and not reaching to the 

 raphe, feebly radiant in the centre of the valve and somewhat convergent at 

 the apices, 8 to 10 in 1 c.d.m., interrupted by a very conspicuous marginal 

 sulcus. Length, 5 to 13 c.d.m. Breadth, 1 to 2 c.d.m. 



Marine. North Sea, Hvidingsoe (Ad. Schm.) 



N. blanda which has been found in various regions of the globe appears to 

 be very rare in the North Sea ; it belongs to a small group of forms of which 

 N. Poivellii (not yet found on our shores) is the type form. 



N. sejuncta Ad. Sch . (Nordsee, p. 87, pi. 1, f. 18*) plate 

 25, fig. 708. 



This species, still imperfectly known, has also been found at Hvidingsoe 

 but it is equally rare. This form is much smaller than the preceding and the 

 stria; reach the raphe throughout. 



II. Radiosae. 



A . Terminal nodules approximate to apices of valves. 



I. Median striae radiate, terminal striae convergent. 

 a. STRI.E APPROXIMATE. 



f Terminal stripe in broken lines 

 f Median 

 striae 



Striae 



in 



continuous 



lines. 



alternately 



long 



and 



short. 



Median 



stripe not 



alternately 



long 



and 



short. 



r 



Valve broadly lanceolate, not rostrate-capitate 



\ Valve broadly lanceolate, rostrate-capitate 



t Valve anceolate, very narrow ..... 



Median striae equally shortened forming a pseudo-stauros ; striae 

 near the central nodule almost straight 



N. oblonga 



N. peregi\na. 

 N. salinarum. 

 N. cincta. 



N. gracilis. 



Apices not 

 rostrate- 

 capitate. 



Apices not conspicuously 

 diminuate-rostrate 



No false 

 stauros 



Nodule 

 surrounded 



by a 

 considerable -{ 

 hyaline area ; 



valve broadly | Apices conspicuously 

 lanceolate. (_ diminuate-rostrate 



Hyaline area very small ; valve narrowly 

 lanceolate ; median striae very 

 radiate .... 



. N. vulpina. 



Apices 

 rostrate- 

 capitate. 



Striae 

 robust. 



f Hyaline area dilated trans- 

 versely, apices very 



robust . 



Hyaline area rounded, apices 

 sub-obtuse 



Striae scarcely visible 



N. viridula. 

 N. radiosa. 



N. cryptocephala. 



N. rhynchocepliala 

 N. gregaria. 



