NAVICULA. 177 



B. Terminal nodules distant from the apices. 



( Valves with median longitudinal portion elevated and 



consequently appearing to be formed of two super- 



, ., posed valves . . . . N. superimposita. 



Valves with | ' * * 



sides equal. | y a i ves w j th on ] v tlle a p| ces elevated . . . N. compressicauda. 



L Valves flat . . N. opima. 



,. , ... f Apices subacute . . . . N. Cesatii. 



V alves with J ^ 



sides unequal. ^ Apices rostrate-capitate . . . . . N. inaequilatera. 



A. Terminal nodules approximate to apices of valves. 



/. Median stricc radiate, terminal stria: convergent. 



A. Striae approximate. 



a. TERMINAL STRIDE IN BROKEN LINES. 



N. oblonga Kutz. (Baa, p. 97, pi. 4, f. 21; H.V.H. Atl, pi. 7, 



f. 1* ; Type No. 76), plate 3, fig. 100. 



Valve linear-elliptic, perceptibly inflated in the median portion, with 

 apices very gently inflated-capitate. Raphe surrounded by a conspicuous 

 hyaline zone dilated circularly round the central and terminal nodules. Costaj 

 robust finely striate transversely, very distant round the central nodule 

 (5 in 1 c.d.m.) then more compact (7 in 1 c.d.m.), radiate, flexuous, lastly 

 the terminal ones still more approximate (8 in 1 c.d.m.), their lines of 

 direction broken abruptly in the middle, radiate from the edge of the 

 raphe, convergent from the edge of the margins. Terminal nodules very 

 robust. Length, 15 to iS c.d.m. 



Fresh water. Rather common and found throughout Europe. 



/>. STRLE IN CONTINUOUS LINES. 

 a. Median strice alternately long and short. 



N. peregrina (Ehr. ?) Kutz. (Baa, p. 97, pi. 28, f. 52 ; H.V.H. 

 Atl., pi. 7, f. 2*; Type No. 77), plate 3, fig. 101. 



Valve broadly lanceolate, with apices very feebly diminuate-rostrate. 

 Raphe surrounded by a narrow hyaline zone dilated round the central nodule, 

 where the blank space forms more or less a square transversely elongate. 

 Costae divided finely transversely, very robust; distant round the central 

 nodule (5 or 6 in 1 c.d.m.) where the long striae are frequently mixed with 

 one or two shorter strife ; median stria? very radiate (6 or 7 in 1 c.d.m.) the 

 terminal ones very convergent, about 8 in 1 c.d.m. Terminal nodules rather 

 robust. Length, 8 to 11 c.d.m. 



Brackish water. Scheldt at Antwerp, and throughout Europe. 



N 



