NAVICULA. 211 



round the central nodule. Striae distinctly granular, radiate, the median ones 

 of unequal length, rather distant, the others very compact, about 9 in 1 c.d.m. 

 Length, 5 to 7 c.d.m. Breadth, 2-5 to 3 c.d.m. 



Marine. Blankenberghe (H.V. H. ; P. Petit). Great Britain (common), and probably or all 

 the North Sea shores. 



This species, says Donkin (Brit. D.), is very variable in size and outline. 

 The dry valve is colourless. 



N. latissima Greg. (T.M.S., 1856, iv., p. 40, pi. 5, f. 4; 

 Ad. Schm. Atl., pi. 6, f. 7*), plate 27, fig. 762. 



Differs from the preceding by its larger size, its more rounded form, and 

 its apices very slightly diminuate, not rostrate. Length, 10 c.d.m. Breadth, 

 5'5 c - dm - 



Marine. Scheldt ; Blankenberghe (H.V.H. ). England, Scotland, Denmark, Finmark, Sweden. 



N. scutelloides W. Sm. (Q.j.m.s., 1856, iv., p. 4, pi. 1, f. 15*), 

 plate 27, fig. 763. 



Valve small, suborbicular. Striae moniliform, strongly radiate, very distant, 

 7 or 8 in 1 c.d.m., reaching to the raphe. 



Fresh water.- Not yet found in Belgium. England, Scotland, Ireland, Bahusie. 

 aa'. MEDIAN STRLE NOT ALTERNATELY LONG AND SHORT. 



b. VALVE WITH COARSE PUNCTA. 



N. granulata Breb. Ms. (H.v.H. Atl., pi. n, f. 15*; in Types 

 Nos. 74, 94, 116, 339, 369, 523, 549, 550), plate 4, fig. 183. 



Valve broad, elliptic or linear elliptic, with median portion sometimes slightly 

 conctricted, apices abruptly attenuate, shortly rostrate. Raphe surrounded by 

 a narrow hyaline zone, enlarged transversely round the central nodule. Striae 

 radiate, 8 in i c.d.m., composed of very coarse puncta. Dry valve of a purple 

 blue colour. Length, 6 to 9 c.d.m. Breadth, 2-5 to 4*5 c.d.m. 



Marine. Ostend, Blankenberghe. England, Scotland, Ireland, France. 



var. maculosa. (A. macu/osa Dotik., Br, Diat., p. 25, pi. 5, f. 1*), 

 plate 27, fig. 767. 



Valve linear-elliptic, narrow ; apices narrowly rostrate. Length, 6-5 

 c.d.m. Breadth, 2 c.d.rn. 



Marine. England (Donk.), usually in company with N. humerosa. 



