NAVICULA. 195 



Valve "sub-elliptical, feebly constricted at the median portion ; with sub- 

 cuneate apices. Central nodule large, quadrangular. Striae, 7 or 8 in 

 1 c.d.m., resolvable into beads, feebly radiant. Length, 6 to 15 c.d.m. 

 Breadth at the median portion, 2 to 2*5 c.d.m. 



Marine. North Sea (England ! Norway.) 



N. Entomon (Ehr.) Ad. Schm. (Nordsee, pi. 1, f. 13*), 

 plate 26, fig. 732. 



Valve elongated, moderately constricted at the median portion, with 

 tongue-shaped segments. Striae indistinctly resolvable, 6 to 8 in 1 c.d.m., 

 feebly convergent at the median portion of the valve, radiant at the apices, 

 occupying only three-fifths of the valve. Sulci very broad, showing a row of 

 scattered beads. Nodule quadrangular, very large. Length, 7 to 15 c.d.m. 

 Breadth of segments, 3 to 4 c.d.m. 



Marine. North Sea, etc. 



N. incurvata Greg. (T.M.S., 1856, iv., p. 44, pi. 5, f. 14; Ad. 



Schm. Nordsee, pi. 2, f. 6*), plate 26, fig. 733. 



Resembles the preceding species, but is much narrower, more elongated, 

 with finer and more approximate striae, about 11-12 in 1 c.d.m. 



Marine. North Sea. 



May this not be a form of the preceding ? 



N. lineata Donk. (Brit. Diat, p. 8, pi. 1, f. 8 ; Ad. Schm. 

 Nordsee, pi. 1, f. 17*), plate 26, fig. 736. 



Valve linear-elliptic, somewhat constricted at the median portion, with 

 rounded apices. Striae irresolvable, feebly radiant, 9 to 10 in 1 c.d.m., 

 crossed in the middle of their length by a smooth longitudinal line, parallel 

 to the margins of the valve. Raphe surrounded by a broad hyaline area 

 showing one or two rows of feebly visible puncta. Central nodule large, 

 subquadrangular. Length, 4 to 8 c.d.m. Breadth, 2 to 3 c.d.m. 



Marine. North Sea (England! Scandinavia Cleve). 



N. subcincta Ad. Schm. (Atl., pi. 13, f. 41*), plate 26, fig. 



737- 



Valve feebly constricted at the median portion, with apices rounded, some- 

 times sub-cuneate ; striae somewhat radiant, considerably distant from the 



