NAVICULA. 205 



Differs essentially from N. Hennedyi in the fact that the sulci are finely 

 dotted, and presenting in the middle a longitudinal arc formed by rows of 5 

 or 6 coarse beads. The valve is also larger and more broadly rounded than 

 in N. Henmdyi\ the striae are marginal, and those near the raphe more distant 

 (10 in 1 c.d.m.), and formed of coarser beads. Length, about 10 c.d.m. 

 Breadth, 6 c.d.m. 



Marine. Scheldt and Blankenberghe (H.V.H.) ; Bahusee (Lagerst. ); St. Brieuc (France) and 

 Solsvig (A. Schm); Ireland (O'M.). This diatom, one of the most beautiful forms of the 

 North Sea, is not excessively rare. 



VII. Asperae. 



f Hyaline space forming a band with cuneate apices, girdle face with almost 



straight margins ; angles verv rounded . . . . N. aspera. 



i 



~\ 



I H\ aline space rounded, not cuneate; girdle face with concave margins, 

 [ angles not rounded . . . . . N. Clepsydra. 



N. aspera Ehr. {Stauroptera aspera Ehr., Amer., p. 134, pi. 1, I., 

 f. T2, etc. ; Stauroneis pulchella IV. Sm. ; H.V.H. Atl., pi. 10, f. 13, and Supp., 

 f. 27* ; in Type No. 101, etc.), plate 4, fig. 165. 



Valve linear-lanceolate or elliptic-lanceolate, with apices obtuse or subacute. 

 Raphe surrounded by a narrow hyaline zone, dilated into a hyaline cuneate 

 band, not reaching the margins of the valve, round the central nodule, which 

 is round, very large, but visible with difficulty. Valve apparently covered with 

 coarse puncta, but which with the best objectives are found to be very fine 

 striae, interrupted in their length, finely divided transversely, regularly radiate 

 up to the apex of the valve, 9 to 10 in 1 c.d.m. Girdle face broad, elongate, 

 with apices truncate, rounded and in the median portion constricted. Length, 

 10 to 18 c.d.m. Breadth, about 2-5 c.d.m. 



Marine. Antwerp (very rare), Blankenberghe, Ostend. England, Scotland, find probably on 

 all the North Sea Coasts. 



N. Clepsydra Donk. (Q.J.M.S., 1861, i., n.s., p. 8, pi. 1, f. 3*), 

 plate 27, fig. 759. 



Differs from the preceding species by finer striae, 10 to 12 in i c.d.m., by 

 the circular hyaline space which surrounds the central nodule, and by the 

 girdle face being much more deeply constricted at the median portion. 



Marine. Sand of seashore. England, Scotland ; France. 



