4 
340 Proceedings of the Royal Irish Academy. 
As to the second, Pfitzer is at variance with most other authors who 
have regarded the forms included under the genus Pinnularia as per- 
fectly symmetrical, and to me they have ever appeared just as symme- 
trical as those of Nayicula. The third characteristic is that which is 
most worthy of notice, but the forms in which the peculiarity has been 
observed are comparativ ely few. So that we are not as yet in a posi- 
tion to regard it as satisfactorily established. For myself I have long 
since regarded the distinction between Navicula and Pinnularia as unsa- 
tisfactory, and have felt obliged to abandon it in consequence of having 
observed forms in which the costate character of the Pinnulariz is 
combined with the moniliform striz of the Navicule. In consequence 
of this there is no alternative but the abandonment of the genus Pin- 
nularia, or the adoption of a new genus to receive these forms in 
which the characteristics of Navicula and Pinnularia are combined. The 
former appears the more satisfactory course, which I have accordingly 
pursued. The forms belonging to this genus are now so very nume- 
rous some more satisfactory grouping of them than that of Smith and 
Ralfs, founded on the outline of the valves, is necessary. Grunow 
has done much towards supplying this desideratum, and, if I have 
succeeded in effecting an improved arrangement, I am indebted to the 
hints supplied by that distinguished naturalist. 
Conjugation has been observed in some species of Navicula. Two 
mother cells produce two sporangial cells or auxospores, as Pfitzer 
designates them, which latter are found to lie in a position parallel to 
that of the former. 
(a.) WVobzles. 
Strie strongly costate, not extending to the median line, but leaving 
a broad, smooth, longitudinal middle space, which is expanded around the 
central nodule, and occasionally extending to the margin. 
Navicula nobilis, (Ehr.) Fresh water. 
Valve large, varying in length from ‘012 to -015; oblong, inflated 
both at the middle and ends; cost broad, converging in the middle, 
and slightly radiate towards the ends; longitudinal free median space 
expanded greatly at the centre and ends. (Plate 30, fig. 1.) 
Kiitz. Bac., p. 98, T. iv., fig. 24. Ralfs, in Pritch., p. 895. Gru- 
now, Verhand. der K. K. Zool. Bot. Gesel., Band x., 1860, p. 515. Cleve, 
Om Svenska och Norska Diat., p. 223.—Pinnularia nobilis, Ehr. 
Proc. Berl. Acad., 1840. Wm. Sm., B.D., Vol. i., p. 54, Pl. xvu.., fig. 
161. Rab. Stissw. Diat., p. 44, T. vi., fig, 2; Rab. Fl. Eur., Alg., sect. 
bp. 209. 
Bantry, Co. Cork. Featherbed Mountain, Co. Dublin. Lugna- 
quilla, Co. Wicklow. Lough Mourne deposit, Co. Antrim. Dromore 
sub-peat deposit, Co. Down. River Bann, at Coleraine, Co. Derry. 
Drumoughty Lough, near Kenmare, Co. Kerry. 
