2 20 NAVICULA. 



robust. Striae 16 or 17 in 1 c.d.m., somewhat convergent at the median 

 portion, feebly radiate at the apices, crossed by a narrow sulcus approximate 

 to the margins of the valve, the outlines of which it follows. Length, 7 to 8 

 c.d.m. Breadth, about 1*5 c.d.m. 



Fresh water Louvain (P.G.). Laviot (Del.), Antwerp (H.V.H.) Aid. Lieg. (De Wild.). 

 Probably not rare, for it has been found throughout Europe. 



var. gibberula. (N. gibberula Kiitz. ; H.V.H. Atl., pi. 12, f. 19*; 

 Caloneis Siltcula {Ehr.) CI. var. gibberula); plate 5, fig. 208. 



Smaller, valve with more marked inflations, apices cuneate. Length, 

 4-5 to 5 c.d.m. 



Like the preceding, throughout Europe. 



N. ventricosa (Ehr.?) Donkin. (Br. D., p. 74, pi. 12, f. 7; 



H.V.H. Atl., pi. 12, f. 24*; Cal. Silicilla (Ehr.) CI. var. ventricosa), plate 

 5, fig. 209. 



Differs from N. linwsa by its inflations being scarcely noticeable, its finer 

 striae, 18 to 20 in 1 c.d.m., and by the stauroneiform hyaline area which 

 surrounds the central nodule. Length, about 6 c.d.m. Breadth, 1*25 c.d.m. 



Fresh water. Antwerp, etc. As in the preceding, 



var. minuta. (H.V.H. Atl., pi. 12, f. 26*); plate 5, fig. 210. 



Very small (2-5 c.d.m. in length), with more marked inflations ; pseudo 

 stauros broader, and apices somewhat cuneate, 21 striae in 1 c.d.m. 



Fresh water. Louvain (P.G.). Ard. Lieg. (De Wild.). 



N. fontinalis Grun. (H.V.H. Atl., pi. 12, f. 33*: Caloneis 

 fascial a ( Lag. ) Cleve) ; plate 5, fig. 211. 



Valve linear, with rounded apices. Raphe surrounded by a lanceolate 

 hyaline zone, enlarged at the middle of the valve into a very broad pseudo- 

 stauroS; Striae feebly radiate, 24 to 26 in 1 c.d.m., crossed by a sulcus almost 

 marginal. Length, about 2*5 c.d.m. Breadth, 0-5 c.d.m. 



Fresh water. Brussels (Delogne). 



XVIII. Affines. 



Raphe with median apices curved like a crook, subparallel, with elongated 

 puncta, interrupted near the margins by a deep sulcus . . . N. Iridis. 



N. Iridis Ehr. (Kiitz. Bac, p. 92, pi. 28, f. 42, N. firma IV. Sm.; 

 H.V.H. Atl., pi. 13, f.i*), plate 5, fig. 212. 



Valve linear elliptic, with rounded apices. Raphe with median apices 

 curved like a crook, in opposite directions, surrounded by a hyaline zone 



