204 NAVICULA. 



N. praetexta Ehr. (Acad.. Berlin, 1840, p. 20; H.V.H. Atl., 

 pi. 9, f. 13*), Plate 4, fig. 159. 



Valve broadly elliptic. Raphe surrounded by a very narrow hyaline 

 zone, enlarged in the form of a stauros near the central nodule. Normal 

 striation in the form of two bands, one at the margin of the valve, the other 

 running the length of the raphe formed of coarse granules with an 

 intermediate space occupied by a broad depression, the bottom of which 

 is irregularly granulated ; normal striae, straight in the middle of the valve, 

 then gradually radiate 6 or 7 in 1 c.d.m. Girdle face quadrangular, oblong, 

 deeply constricted at the central nodule, girdle face showing six longitudinal 

 lines of fine granules, of which the four interior are arranged in pairs. 

 Length, 7 to 9 c.d.m. Breadth, 5*5 c.d.m. 



Marine. Blankenberghe, Scheldt at Antwerp (rare). Scotland, England, Ireland (O'Me.). 

 France, Denmark, Holland. 



N. Hennedyi W. Sm. (S.B.D., ii., p. 93; H.V.H. Atl., pi. 9, 



f. 14 ; Type No. 109), plate 4, fig. 160. 



Valve oval ; raphe surrounded by a very narrow hyaline zone, enlarged 

 into a stauros near the central nodule; stria; finely granular 10 in 1 c.d.m., 

 gradually radiate from the middle of the valve, interrupted on each side by a 

 crescent-shaped depression, the bottom of which is smooth or very finely 

 dotted. Length, about 6 to 7 c.d.m. Breadth, about 4 c.d.m. 



Marine.- -Very rare. Blankenberghe. England, Scotland, Ireland, and on all the North Sea 

 coasts. 



var. clavata (A', clavata Greg., T.M.S., 1856, iv., p. 46, H.V.H. 



Atl., pi. 5, f. 17). 



Differs from the type form by the apices gently subrostrate, and by the 

 depression, which is very narrow. 



Marine. Blankenberghe ; very rare. England, Scotland, Ireland. 



var. nebulosa (N. mbulosa Greg., Diat. of Clyde, p. 68, pi. 1, f. 8 ; 

 Ad. Schni. Atl., pi. 3, f. 14*), plate 27, fig. 755. 



Differs from the type form by less obtuse apices, finer striae (12-14 in 

 1 c.d.m.), which only occupy a narrow marginal band right round the 

 valve. Length, 6 to 9 c.d.m. 



Marine. Not yet found in Belgium, where however it will be. Scotland (Greg.), Ire- 

 land (O'M.), Solsvig (A. Schm.), Marstrand (H.V.H. ). 



N. Sandriana Grun. (in Wien. Verh., 1863, p. 153, pi. 13, f. 5*), 

 plate 27, fig. 756. 



