NAVICULA FIRMA. 3l 
some observers considered a variety of N. firma. I have 
found it in a living state in gatherings associated with the 
latter, with N. affinis and N. amphirhynchus. 
Hab. Fresh water: frequent. River Coquet Northum- 
berland (A. 8. D.). 
Navicula firma, Kiitzing. 
Navicula firma, Kiitz. Bac. p. 92, t. xxi. fig. 10; Ralfs, in Prit. Inf. 
p. 909. 
Navicula firma, var. B and y, Sm. Synop. vol. i. p. 48, and vol. ii. p. 90. 
Navicula amphigomphus, Ehren. Amer. 1843, p. 129, t. IL. i. fig. 8, 
and Mikrogeo. numer. figs.; Kiitz. Bac. p. 93, t. xxviii. figs. 
40 & 41; Rabeuh. Siissw. Diat. p. 38, t. vi. fig. 47, and Europ. 
Diat. p. 176; Ralfs, in Prit. Inf. p. 908. 
Pinnularia amphigomphus, Ehren. Amer, t, IL. i. fig. 27, and Mikrogeo. 
t. xiv. fig. 11? 
Navieula dilatata, Ehren, Amer. 1848, p. 180, and Mikrogeo. numer. 
figs,; Kiitz. Bac. p.99; Rabenh. Siissw. Diat. p. 37, and 
Europ. Diat. p. 173; Ralfs, in Prit. Inf. p. 908, 
Navicula affinis, var. b, Rabenh. Europ. Diat. p. 196, and var. 8. am- 
phirhynchus, Grunow, in Wien. Verh. 1860, p. 544, t. iii. fig. 5. 
Navicula pannonica, Grunow, in Wien. Verh. 1860, p. 541, t. ii. fig. 40, 
and Rabenh, Europ. Diat. p. 174 ? 
Plate V. fig. 7. 
V. linear, with cuneate, subacute, or obtuse extremities, or 
linear-elliptical, attenuated towards the obtuse extre- 
mities ; strie fine, granular, about 40 in :001", trans- 
verse, reaching to the median line, shortened opposite 
the central nodule, and interrupted by longitudinal 
wavy lines near the margin; colour brownish. 
In consequence of being subject to considerable variation 
in outline, the position of this species is in a state of great 
confusion. Kiitzing’s typical form was found in the well- 
known fossil diatomaceous earth from Santa Fiore in Italy ; 
as it occurs in this deposit its outline is almost linear, with 
cuneate, obtuse, or subacute, extremities. Ehrenberg, 
