34 NAVICULEZ. 
the easy identification of species that they should be sepa- 
rated from each other. 
A. Extremities capitate or subcapitate. 
1. Valve elliptical. 
Navicula amphirhynchus, Ehrenberg. 
Navicula amphirhynchus, Ehren. Amer. 1843, p. 129, t. II. i. fig.10 &c. ; 
Kiitz. Bac. p. 95, t. iv. fig. 18, t. xxi. fig. 11, and t. xxviii. 
fig. 47; Rabenh. Siissw. Diat. p. 40, t. vi. fig. 50; Sm. Synop. 
vol. i, p. 51, pl. xvi. fig. 142; Ralfs, in Prit. Inf. p. 901, pl. xii. 
fig. 6. 
Navicula producta, Smith, Synop. vol. i. p. 51, pl. xvii. fig. 144; Ralfs, 
in Prit. Inf. p. 902, pl. vii. fig. 66; Grunow, in Wien. Verh. 
1860, p. 548, t. ii. fig. 35. 
Navicula affinis, var. c, Rabenh. Europ. Diat. p. 196, var. a. genuina, 
Grunow, in Wien. Verh. 1860, p. 543, t. iii. figs. 2a & 6, & 3, 
Plate V. fig. 9. 
V. elliptical or linear, with produced capitate extremities ; 
striz fine, distinct, granular, about 40 in 001", trans- 
verse in the middle, oblique towards the extremities, 
reaching to the median line, slightly shortened oppo- 
site the central nodule, and interrupted midway be- 
tween the median line and the margin by one or more 
undulating longitudinal lines. Dry valve yellowish 
brown. 
Had. Fresh water: frequent. 
Navicula spherophora, Kiitzing. 
Navicula spherophora, Kiitz, Alg. exs. no, 84, Bae. p. 95, t. iv. fig. 17; 
Sm. Synop. vol. i. p. 52, pl. xvii. fig. 148; Rabenh. Siissw. 
Diat. p. 40, t. vi. fig. 65a, and Europ. Diat. p. 191; Ralfs, in 
Prit. Inf. p. 899. 
Plate V. fig. 10. 
V. elliptical-lanceolate, deeply constricted into produced, 
