202 NAVICULA. 



are less marked, and are only apparent with oblique illumination. Length, 

 up to 6 c.d.m. Breadth, 2*5 c.d.m. Valve excessively delicate, apparently 

 hyaline under the best dry objectives. 



Marine. Very rare? On the sands at the coast at Cresswell and Boulmar (England ; Donkin). 

 Curabrae (Scotland, Coll. W. Arnott in Coll., H.V.H.). 



V. Lyratae. 



f Sulci more or less divergent, equally broad through- 

 out . . . . . N. Lyra. 



Sulci straight or somewhat convergent, much broader 



at their median portion than at the apices . N. spectabilis. 



Blank space surrounding the raphe, with median 

 apices clavate . . . . , N. forcipata. 



, , f Central nodule surrounded by a nar- 



Blank space , . r , . J ,- 



Valve with coarse 

 puncta. 



Valve with fine 



puncta; sulci K- row.hyahne area ; sulci not reaching 



J surrounding ' J a 



nver- \ 



gent. 



strongly conver- ~\ jV rounoing to the apex of the valve . . N. abr^pta. 



j 



with median 



apices not 



clavate. 



Central nodule surrounded by a 

 broad hyaline area ; sulci reaching 

 almost to the apices . . N. pygmaea. 



A. Siricz formed of coarse granules. 



N. Lyra Ehr. (KUtz. Baa, p. 94, pi. 28, f. 55; h.v.h. Atl., 

 pi. 10, f. 1 and 2*; Type No. no), plate 4, fig. 161. 



Valve broadly elliptic, with apices often somewhat diminuate subrostrate. 

 Raphe surrounded by a narrow hyaline zone, dilated into a stauros round the 

 central nodule. Striae formed of coarse puncta, about 7 to 9 in 1 c.d.m., 

 more and more radiate from the median portion, and interrupted on each side 

 of the raphe by a sulcus, the bottom of which is generally smooth, but where 

 the striae continue sometimes more feebly, incurved at the middle where it 

 rejoins the stauroneiform hyaline space, in such a manner that the entire 

 smooth spaces have the appearance of a lyre. Length, 11 to 12 c.d.m. 

 Breadth, about 5 c.d.m. 



Marine. Blankenberghe (rare). Found on all the North Sea coasts. 



N. spectabilis Greg. (Diat. of Clyde, p. 9, pi. 1, f. 10*), plate 

 27, fi g- 757- 



Probably only a form of the preceding, from which it differs essentially in 

 that the sulci are at least twice as broad, and are finely dotted. 



Marine. Not yet found in Belgium. Scotland, Ireland, France, Sdlsvig, Cuxhaven, 

 Marstrand. 



