NAVICULA. 189 



IV. All the Stria: perpendicular to the raphe. 

 N. directa W. Sm. ! (S.B.D., i., p. 56, pi. 18, f. 172*; sub 



Pinnularia ; in Type No. 394) ; plate 25, fig. 722. 



Valve linear-lanceolate, infinitesimally attenuate up to the acute apices. 

 Striae about 7 in 1 c.d.m., exactly perpendicular to the raphe, which they 

 almost touch. Length, 6 to 9 c.d.m. 



Marine. England (W. Sm. !). Scotland (W. Arn. !). Ireland (O'Meara). This diatom is 

 not common, but will certainly be found in other parts of the North Sea. 



var. subtilis. {Finn, subtilis Greg., Clyde, p. 488, pi. 9, f. 19*) ; plate 

 25> fi g- 7 2 3- 



More rhomboidal and at the apices more acute than the type form ; 9 

 or 10 delicate costae in 1 c.d.m. 



Marine Ccast of Scotland (Lamlash Bay, Greg. 1. 



N. Northumbrica Donk. (Q.J. M.S., 1861., i., n.s., p. 9., pi. 1., 



t. 5 ; id., Brit. Diat, p. 54, pi. 8, f. 1* ; in H.V.H.'s Types oi Syn., Nos. 13, 

 116, and 369) ; plate 25, fig. 726. 



Valves narrowly lanceolate, with apices attenuate-acute. Striae about 

 7 or 8 in 1 c.d.m., very delicate and perpendicular to the raphe, the median 

 somewhat coarser and more distant. Central nodule opaque, very con- 

 spicuous. Girdle face very broad, subquadrangular, somewhat concave from 

 the sides of the valve. Length of valve, about 5^5 to 6-5 c.d.m. Breadth, 

 somewhat more than 1 c.d.m. 



Marine. England, Ireland, France. 



B. Terminal nodules distant from the apices of the valve. 



1. Valve with equal sides. 



N. superimposita Ad. Schm. (Nordsee, p. 90, pi. 2, f. 34*), 

 plate 25, fig. 724. 



Valve lanceolate or sublanceolate, with apices rounded, more or less 

 capitate, with longitudinal median portion considerably super-elevated, in such 

 a manner as to simulate a second smaller valve placed on the lower. Striae 

 robust, radiant, shortened, 4 or 5 in 1 c.d.m., not reaching to the raphe, and 

 leaving a considerable stauroform hyaline space round the central nodule. 

 Length, 9*5 to 11*5 c.d.m. 



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



