20D NAVICULA. 



N. notabilis Grev. (T.M.S., 1863, iii., p. 18, pi. 1, f. 9; Sch. Atl., 

 pi. 8, f. 46-47*), Piate 26, fig. 750. 



Valve oval-elliptic, with sulci scarcely attenuate near the median portion. 

 Costae robust, 10 in 1 c.d.m., not showing small beads in the intercostal 

 spaces, interrupted by two broad and deep depressions, one at the middle of 

 their length, the other between their apices and the sulcus. Marginal costae 

 in addition interrupted by one or two narrow sulci in a manner to simulate 

 beads. Length, 3 c.d.m. Breadth, abjut 2 c.d.m. 



Marine. Not yet found in Europe. 



var. expleta Ad. Schm. (Nordsee, p. 88, pi. 2, f. n ; Atl., pi. 8, 

 f. 48-5*), P late 26 ' fi g- 75 1 - 



The median depression of the cos! a; disappears, and these are trans- 

 formed into a series of false puncta forming longitudinal lines in zig-zag. 



Marine Maritime Scheldt (H.V.H.). Hvidingsoe (Ad. Schm.). English Channel. 

 Estuary of Shannon, Ireland 



The form found in the Scheldt is less oval and more subquadrangular than 

 the type form figured by Dr. A. Schmidt. 



N. advena Ad. Schm. (Atl., pi. s, f. 29* ; H.v.H.'s Types No. 

 197), plate 26, fig. 752. 



Valve longly linear-elliptic, sometimes somewhat constricted at the median- 

 portion. Costre 9 in 1 c.d.m., delicate, parallel, continuing into the sulci. 

 Central nodule of medium size, with straight horns, approximate. 



North Sea. Scotland (Cumbrae !) 



var. parca. (Ad. Schm. Atl., pi. 8, f. 20. 21, 22*), plate 26, fig. 753. 

 Smaller and more delicate ; valve longly elliptic. 

 Marine. North Sea. 



A A. Valve moniliform, not furnished with costcc. 



N. littoralis Donk. (Brit. D., p. 5, pi. 1, f. 2; H.V.H. Atl. Supp., 

 f. 25* in Type No. 104), plate 4, fig. 154. 



Valve oval. Nodule very elongate. Raphe not surrounded by a hyaline 

 area. Sulci completely straight, and quite approximate to the raphe. Striae 

 14 in 1 c.d.m., perpendicular to the raphe at the median portion, becoming 

 more and more radiate near the apices. Length, about 4 to 5 c.d.m. 



Marine. Blankenberghe (very rare), England. 



