NAVICULA. 169 



b. Valves undulate or constricted. 



f Valve rather broad, with median f Apices strongly rostrate-capitate . N. mesolepta. 



inflation not much larger than -j 

 the terminal. ^ Apices scarcely diminuate-rostrate . N. Legumen. 



: Median inflation much larger than the terminal inflations; valve very narrow N. polyonca. 



Median inflation much smaller than the terminal inflations . . . N. claviculus. 



II, Terminal nodules dilated laterally like a hook. 



Valve very inflated at the median portion, apices subcapitate costae very 



robust. ......... N. bumilis.* 



b' . Striation interrupted by a marginal sulcus. 



f Striae not reaching to the raphe and leaving a large hyaline space round the 

 central nodule . . . . . . . . N. blanda. 



j Strice reaching everywhere to the raphe and central nodule . . . N. sejuncta. 



* For facility in determination we have left, in the Table of the Pinnularieae, the ;V. 

 costulala and A r . humilis, which belong to the Radioseae, but are very difficult to resolve into 

 beads. See these species among the Radiosea-. 



i. Valves neither undulate nor constricted in the middle. 



A. Costae very distant and very robust. 



* WITHOUT A FALSE STAUROS. 



N. lata Breb. ! (W. Sm., S.B.D. 55, sub. Pinnularia, pi. 18, f. '67 . 

 H.V.H. Ad, pi. 6, f. 1, 2*; Type No. 61), plate 2, fig. 76. 



Valve linear, with median portion slightly inflated, apices obtuse, broadly 

 rounded. Costae very robust, distant, 4 to 5 in i c.d.m., not reaching to the 

 raphe, and leaving a dilated hyaline space round the central nodule ; costae 

 feebly radiate at the middle of the valve, and changing direction imperceptibly 

 towards the apices. Length, about 6 to 1 1 c.d.m. 



Fresh water in mountainous regions. Not yet found in Belgium. England, France. 



N. alpina Ralfs. (in Pritch. Inf., p. 906; W. Sm. S.B.D. i., p. 55, 

 pi. iS, f. 168* ; H.V.H. Type de Syn. No. 51), plate 25, fig. 705. 



Valve broadly lanceolate-elliptic, with apices obtuse. Costae very robust, 

 distant, radiate, 2-5 to 3 in 1 c.d.m., resting very distant from the raphe, and 

 not symmetrically on each side of the valve. Raphe and nodules very robust. 

 Girdle face quadrangular, elongate, showing on the connecting membrane two 

 distant lines of fine elongate puncta. Length of valve, 10 to 20 c.d.m. 



Fresh water of subalpine regions. Scotland, France. 



