10 NAVICULE. 
line; striae coarse, much inclined, and divided by a 
doubly incurved longitudinal line into two sections, the 
inner narrow and faint, the outer broad, conspicuous, 
and costate, or obscurely granular. 
Hab. Marine. Lamlash Bay Isle of Arran (Prof. Gre- 
gory). 
Navicula pygmza, Kiitzing. 
Navicula pygmea, Kitz, Spec. Alg. p.77; Rabenh. Siissw. Diat. p. 39, 
and Europ. Diat. p. 184; Sm. Synop. vol. ii, p.91; Ralfs, in 
Prit. Inf. p, 899, 
Navicula minutula, Smith, Synop. vol. i. p. 48, pl. xxxi. fig. 274, 
Plate I, fig. 10. 
Frustule minute. V. elliptical or oblong-elliptical, hyaline ; 
median line faint; striz indistinct, very fine (80 in 
001", Smith), and crossed by a faint, doubly incurved 
longitudinal line. 
Hab. Brackish water, frequent. 
B. Extremities rounded or produced; strie@ on each half of the valve 
separated into two bands (a marginal and a median) by an unstriated 
longitudinal area, extending between the extremities of the valve ; 
median band narrow and interrupted by the central nodule. 
1. Extremities rounded. 
Navicula pretexta, Ehrenberg. 
Navicula pretexrta, Uhr. Berlin, 1840, p. 20; Kiitz. Bac. p. 98; Greg. 
Diat. of the Clyde, p. 9, pl. i. fig. 11; Ralfs, in Prit. Inf. p. 898 ; 
Rabenh. Europ. Diat. p. 183. 
Pinnularia pretexta, Ehr. Mikrogeo, t. xix. fig. 28, 
Plate II. fig. 1. 
Frustule large. V. broad-oval ; striz coarse, granular, 8 
to 10 in 001"; marginal band narrow, with an inde- 
