210 



NAVICULA. 



N. elegans W.Sm. (S.B.D., i., p. 49, pi. 16, f. 137*), plate 27, 

 fig. 761. 



Valve lanceolate, with apices diminuate, sub-acute. Central nodule sur- 

 rounded by a considerable hyaline area. Stria; not reaching to the raphe, 

 radiate, undulate ; apparently costiform, very vigorous, 6 or 7 in i c.d.m. 

 Length, 7 to n c.d.m. Breadth, 3 to 3*5 c.d.m. 



Brackish water. Not yet found in Belgium. Rather common in England. Marstrand ! 

 (Sweden). 



XI. Perstriatse. 



r r 



0) 



3 



I 3 s 

 a o 



o'rt 



o 



> 



Valv 



T3 



u 

 '_> 



3 

 T3 

 O 



(X 



< 



Median 

 strire 

 alter- 

 nately 



long and 

 short. 



Valve large, elliptic, 



oval, or 



subquadrangular. 



f Apices elongate, ros- 

 I trate 

 j 



! Apices very gently 

 diminuate, not ros- 

 t trate 



( Valve small, suborbiculate 



r 



Striae 

 not 

 alter- 

 nately 

 long and 

 short. 



Valves 



with 



coarse 



puncta. 



( Valve with rounded 



Apices ! h >' aline st5ace 

 somewhat \ Valve wkh nan . ow 

 rostrate. elongated pseudo- 



l_ stauios . 



Apices sub-acute 



I 



Valve 



regularly 



elliptic. 



Scattered puncta in 

 centre of valve 



j Striae with distant 

 l_ puncta . 



Valve with fine puncta, valve regularly elliptic . 

 _ Apices produced, rostrate . 

 e having two lunate sulci near the central nodule 



N. humerosa. 



N. latissima. 

 N. scutelloides. 



N. granulata. 



N. Scandinavica. 

 N. marina. 



N. Baileyana. 



N. fraudulenta. 



N. Scutum. 



N. pusilla. 



N. Schumanniana. 



I. Valve without lunate sulci near the central nodule. 



a. Apices not produced rostrate. 



a'. MEDIAN STRL ALTERNATELY LONG AND SHORT. 



N. humerosa Breb. (in w.Sm., S.B.D., ii., p. 93; H.v.H. Atl., 



pl. 11, f. 20*; Type No. 117), plate 4, fig. 182. 



Valve linear-elliptic, with apices somewhat abruptly constricted, attenuate. 

 Raphe surrounded by a narrow hyaline zone, somewhat dilated transversely 



