194 



NAVICULA. 



N. Weissflogii A. Schm. (Uber N. Weissflogii and N. 

 Grundkri in Giebel's Zeitschr, 1873; H.V.H. Atl. Suppl., f. 21), plate 3, 

 fig. 148. 



This beautiful species, very similar to N. didyma, differs from it essentially 

 by its strange constriction, by the band not being moniliform in the middle of 

 the valve and by the arrangement of the beads near this band, and of which 

 the entirety forms a St. Andrew's Cross. Stride about 7 in 1 c.d.m. Length 

 about 4 - 5 to 5 c.d.m. 



Marine. Blankenberghe ; rather rare. 



N. Bombus Ehr. (Abh., 1844; H.V.H. Atl. Suppl. , f. 22*; in 

 Type No. 104), plate 3, fig. 149. 



Rather large ; valve deeply constricted with subcordate lobes ; raphe 

 surrounded by a broad hyaline zone, with sulci showing small beads in irregu- 

 larly curved rows. Striae 6 in 1 c.d.m. with coarse beads; those on the 

 margin of the valve elongate and much larger than the others. Median 

 portion of the valve hyaline, showing only some large isolated beads. Length, 

 about 8 c.d.m. 



Marine. Blankenberghe (rare). Found in France, England, Scotland, Ireland and Norway. 



N. vacillans Ad. Schm. (Atl., pi. 8, f. 61 ; H.V.H. Atl, 



plate 9, f. 9*), plate 3, fig. 150. 



Very small, valve narrowly elliptic, gently attenuate at the median 

 portion. Central nodule large, raphe surrounded by a narrow hyaline 

 zone. Sulci approximate to raphe, almost straight, feebly flexed towards 

 the exterior round the central nodule. Striae finely punctate transversely, 

 feebly radiate, about 16 in i c.d.m. Girdle face constricted in the 

 middle. Length, about 2 c.d.m. 



Marine. ^Ostend (H.V.H.) ; very rare. 



The above form constitutes A^ vadllans forma minuta. The true type is 

 from 4 to 6 c.d.m. in length. 



N. constricta Grun. (Verh., i860, p. 535, pi. 3, f. 18; in h.v.h. 



types No. 103 ; N. musca Donk.; N. Donkinii Ad. Schm. Atl., pi. 12, f. 63*), 

 plate 26, fig. 731. 



