O’Mrara—Report on the Irish Diatomacee. 359 
Navicula decipiens, N.S. Marine. 
Valve narrow, elliptical, rounded at ends; length :0030, breadth 
0008. Strie fine, close, slightly radiate; in some lights apparently 
punctate; seemingly disappearing in the middle, and presenting the 
appearance of a narrow stauroform band, extending to the margins; 
this however is deceptive. (Pl. 31, fig. 6.) 
Tide-pools, Galway Bay, near the town of Galway. 
Navicula tumens. (Wm. Smith). Brackish or marine. 
Valve: elliptical; ends produced. Length from :0024 to -0040, 
breadth from -0010 to 0015. Strie fine, punctate, slightly radiate ; 
when not exactly in focus appearing to be moniliform. (PI. 31, fig. 7.) 
Smith has correctly described the character of the striz in this 
species; but the figure represents the strize as they appear when not 
in focus. 
Donkin, N. H., Brit. Diat., p. 15, considers this form as identical 
with Navicula rostrata, Ehr., and Navicula sculpta, Ehr. These 
forms it appears were found by Donkin in the Bergmehl of Santa 
Fiore, and in the fossil deposit of Franzensbad, which I believe are 
both fresh watcr deposits, though that author assigns Navicula ros- 
trata to brackish localities. The form under consideration has been 
found by Smith only in brackish water; and I have found it only in 
localities decidedly brackish or marine. However similar the forms 
may be, they seem to me perfectly distinct, and distinguishable by 
this feature, that in Navicula tumens the strie run uninterruptedly 
from the margin to the longitudinal sulci, whereas in N. rostrata they 
are interrupted, and present an unstriate space between each sulcus 
and the ends of the strie. Wm.Sm., B. D., Vol.i, p. 52, Pl. xvii., 
fig. 150. Ralfs, in Pritch., p. 900. Grunow, Verhand. der K. K. Zool. 
Bot. Gesell., Band x., 1860, p. 541., Rab. Fl. Eur. Alg., sect. i., p. 192. 
Salt ditch, near Newtownlimavady Junction, Co. Londonderry. 
Salt ditch, near the town of Galway. Seaweeds, Salt Hill, Co. 
Dublin. Salt ditch, Breaches, Co. Wicklow. Lough Gill, Co. Kerry. 
Nawicula rostrata. (Ehr.) Fresh or brackish water. 
Valves elliptical, produced into long rounded apices; length 
0046, breadth -0015. Striz punctate, slightly radiate, disappearing 
in the middle of the space between the margin and the longitudinal 
sulcus, and appearing again upon the edge of the sulcus. (Pl. 31, fig. 8.) 
There is some doubt as to whether this species belongs to fresh 
or brackish water. The fact that Donkin identified the form, so well 
delineated by him, with specimens from the Santa Fiore deposit, as well 
as that of Franzensbad, would seem decisive as to its proper habitat 
being in fresh water. The localities, however, to which he has 
assigned the species found by him in a living state are brackish; 
