376 Proceedings of the Royal Irish Academy. 
and distinguished by the apparent absence of strie.” If the valve be 
examined in a dry state, the longitudinal strie are distinct, but much 
less numerous and distinct than in Navicula affinis; the margin 
also, instead of being perfectly linear as it is in the last named species, 
is slightly elliptical. 
Lough Mask, near Tourmakeady, Co. Mayo. Featherbed Moun- 
tain, Co. Dublin. 
Navicula rostellum, (Wm. Sm.) Fresh water. 
Valves broadly elliptical; ends produced into very short narrow 
apices; longitudinal sulci parallel to median line distinct; strie 
obscure; length -0020; breadth -0010. (Plate 31, fig. 53.) 
Wm. Sm., B. D:, ‘Vol. .a., p..93.'. Ralts, im Patch:, p;.900. 9Gra- 
now, Verhand. der K. K. Zool. Bot. Gesell., Band x., 1860, p. 550, 
T. iv., fig. 10. This form, as described by Grunow, is narrower, and 
the apices much wider than in my specimens; the transverse striz as 
described, are very fine and parallel, but as my specimens were mounted 
in balsam, I could not detect the strie. Donkin, N. H. Brit. Diat., 
p. 40, Pl. vi, fig. 7. Rab. Fl. Eur. Ale. sect. 1., ps 195.) The jas 
named author describes the striz as very delicate and parallel.—Navi- 
cula apiculata, Gregory Q.J.M.S., Vol. iv., 1856, Pl.i., fig. 13, who 
attributes the form to Wm. Smith. 
Killakee, Co. Dublin. 
Nawvicula levissima, (Kiitz.) Fresh water. 
Valve colourless, slightly expanded in middle, slightly constricted 
towards the broad rounded ends; median line strongly developed; 
transverse striz very fine, slightly radiate ; longitudinal strize distinct ; 
intermediate free space narrow, except in the middle, where some- 
times it seems to expand in a short narrow stauroform band; at the 
extreme end a distinct transverse line is noticeable at right angles 
with the median line; length -0015, breadth 0004. (Plate 31, fig. 54.) 
Kitz: ‘Bae? p..96, 1. xo.) fie 14. Wane, im, ola ae 
p- 91. Grunow, Verhand. der K. K., Zool. Bot. Gesell., Band x., 
1860; p. 549, T. ty.; fig? 5. Rab. Bi Mur Ale jseet> 2, pecs 
Ponkin, N. HH. ButoDiatip.28, Piws he. 2: 
Lower Lake, Killarney, Co. Kerry. Derrylane Lough, Co. Cavan. 
Lough Neagh, near Antrim town. Ulster Canal, near Poyntzpass, 
Co. Armagh. lLoughbrickland Lake, Co. Down. River Bann, near 
Coleraine, Co. Derry. Trinity College Botanic Gardens, Co. Dublin. 
Killeshin, Queen’s Co. Feighcullen, Co. Kildare. 
Nawvicula oblongella, (Naegeli?) Fresh water. 
Valve small, linear, elliptical; ends rounded; longitudinal sulci 
close to median line, strongly developed, parallel; transverse strie 
