24 NAVICULEE. 
Hab. Brackish water : frequent. Pool Bay (Prof. Smith) ; 
Lancashire (Mr. Johnston); near Hull (Mr. Norman) ; 
R. Blyth, Northumberland (A. S. D.). 
Navicula subsalina, Donkin. 
Navicula Amphisbena, var. 8, Smith, Synop. vol. i. p. 51, pl. xvii. 
fig. 1478; Ralfs, in Prit. Inf. p. 899, pl. ix. fig. 141, non 
pl. vii. fig. 72; Rabenh. Europ. Diat. p. 191, confusa cum 
N. Amphisbena. 
Plate IV. fig. 2. 
V. elliptical, or elliptical-lanceolate, with produced, obtuse 
extremities ; striz distinct, about 30 in ‘001", slightly 
oblique, shortened in the middle, and lengthened to- 
wards the extremities, so as to leave a broadly lanceo- 
late median blank space. 
This species has long been confounded with N. Amphis- 
bena, of which, on very insufficient grounds, it has been 
considered a variety peculiar to brackish water; it is, how- 
ever, essentially different, in its much coarser striz, in the 
outline of its extremities, and larger size, independently of 
habitat. The assertion of the late Prof. Walker Arnott 
(Quart. Micr. Journ. vol. vii. p. 176), that “N. Amphisbena 
occurs in fresh water, brackish water, and in the sea” (this 
being the brackish-water, and NM. brevis, Greg., the salt- 
water variety), appears to me to be purely hypothetical. 
By careful observation I have been unable to detect the 
slightest approximation towards an intermediate state be- 
tween N. Amphisbena and its supposititious varieties ; con- 
sequently I have, without hesitation, separated the present 
species from it. 
Hab. Brackish water: frequent. 
