N. Liber. 



22 2 NAVICULA. 



XIX. Lineares. 



f c , , , f Margins straight, apices rounded 



Stnneextendingover | 6 . 



the whole valve . *| ,^ . , . .. ,. ... .. 



l_ Margins excavated at the median portion . . var. bicuneata. 



C Pseudo-stauros very broad ; 13-16 in 1 c.d.m ; 



Striae interrupted by J sulcus conspicuous . . N. consimilis. 



a pseudo-stauros . ~j D , . . . , 



^ I Pseudo-stauros narrow, 19-21 striae in 1 c.d.m. ; 



{ sulcus less visible . . . . . N. aemula. 



N. Liber W. Sm. (S.b.d., i., p. 4 8, pi. 16, f. 133; h.v.h. Atl., 



pi. 12, f. 36* ; Type No. 137), plate 5, fig. 219. 



Valve linear narrow, with rounded apices. Raphe with a hyaline and but 

 slightly marked zone. Central nodule surrounded by a small rounded hyaline 

 area ; terminal nodules somewhat distant from the apices, curved like a 

 comma. Striae fine, parallel, about 18 in 1 c.d.m., crossed by a longitudinal 

 sulcus flexed towards the margin at the median portion. Length, about 

 8 c.d.m. Breadth, 1.5 c.d.m. 



Marine. Washings of mussels (Deby.) Blankenberghe, Scheldt (H.V. H. ). England (W. Sm., 

 Kitton, Comber, Norman). Ireland (O'Meara), and probably on all the North Sea Coasts. 



var. linearis. (H.V.H. Atl., pi. 12, f. 35), plate 5, fig. 220. 



Much smaller and narrower. Length, 5.5 c.d.m. Breadth, about 

 1 c.d.m. 



var. bicuneata Grun. (N. maxima Greg., Q.J. M.S., 1856, hi., p. 41, 

 pi. 4, f. 19 ; T.M.S., 1856, iv., p. 39, pi, 5, f. 2*),' plate 35, fig. 910. 



Differs from the type form by its greater breadth, by its sides being 

 somewhat excavated at the median portion, and its apices somewhat 

 cuneate. 



Valves large, broadly linear, oblong, with margins gently excavated at 

 the median portion, apices cuneate, obtuse. Transverse striae 13-14 in 

 1 c.d.m., reaching to the raphe, parallel, crossed by a sulcus at the 

 middle of their length. Length, 10 c.d.m. Breadth, 2 to 2.5 c.d.m. 



Marine. Scotland (Gregory, Donkin), Ireland (O'Meara). 



Mr. Grunow believes that this form ought to be considered as a variety 

 of N. Liber. 



N. COnsimilis Ad. Schm. (Nordsee Diat., p. 91, pi. 2, f. 46*), 

 plate 27, fig. 773. 



Has been found in the North Sea by Dr. A. Schmidt. It is distinguished 

 from JV. Liber by stronger strise (13 to 16 in 1 c.d.m.), interrupted in the 

 median portion of the valve by a very broad hyaline space stauroneiform, and 

 again by more robust sulci, 



