174 NAVICULA. 



2. Valves bi-undulate or tri-undulate, or conspicuously constricted in 

 the median portion. 



N. mesolepta Ehr. (Am. iv., n. 4 W ; h.v.h. Atl., pi. 6, f. 



io and ii*; Type No. 68), plate 2, fig. 96. 



Valve linear-oblong, tri-undulate, with apices rostrate-capitate ; striae 

 gradually shortened towards the central nodule, the median ones very radiate, 

 the terminal convergent, 10 to 14 in 1 c.d.m. Length, 3 to 6 c.d.m. 



Fresh water. Almost everywhere. 



Var. Termes (N. Termes, Ehr., H.V.H. Atl., pi. 6, f. 12, 13*), 

 plate 2, fig 97. 



Valve with median inflation replaced by a slight constriction ; striae 

 absent in the middle of valve, thus forming a pseudo-stauros. 



Fresh water. Antwerp, Louvain, etc. (H.V.H. ), Ard Liege (De. Wild), 



N. Legumen Ehr. (Mikrog, various figures H.V.H., pi. 6, 

 f. 16* ; Type No. 69), plate 2, fig. 98. 



Valve linear, gently tri-undulate, with undulations sometimes scarcely 

 noticeable ; apices diminuate-rostrate, scarcely capitate ; raphe surrounded 

 by a broad hyaline area, considerably dilated round the central nodule ; 

 striae about 11 in 1 c.d.m., very radiate at the median portion, very 

 convergent towards the apices of the valve. Length, 8 to 10 c.d.m. 



Fresh water. Liresse (Delogne). Found throughout Europe. 



N. polyonca Breb. ! (in Kiitz. Sp. Aig., p. 85 ; h.v.h. Atl. 



Supp., f. 14*), plate 2, fig. 99. 



Valve linear-narrow, tri-undulate, with median inflation much stronger 

 than the others ; apices strongly inflated-capitate ; raphe surrounded by a 

 large hyaline zone, which widens into a false stauros at the median 

 portion; striae about 12 in 1 c.d.m., shortened at the median portion where 

 they are radiate, becoming very convergent at the apices. Length, 6 to 8 c.d.m. 



Fresh water. Rare. Liresse (Delogne), Scotland, Ireland, France. 



N. claviculus Greg. (Diat. of Clyde, p. 6, pi. 1, f. 5*), plate 



25, fig- 79- 



Valve sublinear-narrow, feebly inflated at the median portion, more 

 strongly inflated from and after the median portion, and this up to the 

 apices which are rounded obtuse. Striae not reaching to the raphe ; 

 only slightly or not radiate, about 14 in 1 c.d.m ; absent at the median 

 inflation. Length of valve, 3-5 to 5 c.d.m. Breadth, about 1 c.d.m. 



Marine. Scotland, Ireland, Jutland, Bahusie. 



