402 Proceedings of the Royal Irish Academy. 
ments on either side of the median one wider than they appear in my 
specimens. Schmidt, Atlas der Diat., T. xu., fig. 51. In outline, 
this figure exactly represents the present species; the striation, how- 
ever, seems different. 
Arran Islands; Stomachs of Ascidians, Broadhayen Bay, Co. Gal- 
way. 
Navicula didyma, (Ehr.) Marine. 
Valves slightly constricted ; median compartment wide, inflexed 
at the ends, greatly constricted in the middle ; compartments on either 
side very narrow, exhibiting a row of moniliform dots on the inner 
margin; marginal striate band broad; strie radiate throughout, closely 
moniliform; length about ‘0030, breadth :0011; breadth at the con- 
striction 0010. (Plate 33, fig. 29.) 
Kiitz. Baec., p. 100, T. iv., fig. 7, T: xxvui., fig. 75. _In the former 
figure, the compartments at either side of the median one are repre- 
sented as much wider than in my specimens; in the latter figure the 
striz are represented as running up to the outer margin of the median 
compartment, the compartments at either side being thus wholly 
obliterated. Kitzing attributes the species to Ehrenberg. Wm. Sm., 
B. D., -Vol...1.5: p.. 53, Pl xvii... fie. 04. Ralls, am Priteh > pases 
Pl. xu., fig. 15. Ralfs’ figure of the species, Pl. vu., fig. 61, 1s more 
like Navicula interrupta than Navicula didyma. Grunow, Verhand. 
der K. K. Zool. Bot. Gesell., Band x., 1860, p. 530. Cleve, Om Svenska 
och Norska Diat., p. 225. Donkin, N. H. Brit. Diat., p. 51, Pl. yu., 
fig. 8. 
The form described by Rabenhorst as Pinnularia didyma, Siissw. 
Diat., p. 46, T. vi., fig. 26, is probably the same as the present spe- 
cies, but if so, its occurrence in fresh water must have been casual. 
Bannow, River Slaney, at Killurin, Tacumshane, Co. Wexford. 
Malahide, Portmarnock, Piles of wooden bridge, Dollymount Strand, 
Co. Dublin. Lough Foyle, Co. Derry. Salt-marsh, near town of 
Wicklow. Kilkee, Co. Clare. Arran Islands ; Stomachs of Ascidians, 
Roundstone Bay; Stomachs of Ascidians, Broadhaven Bay,  sea- 
weeds near Westport, Co. Galway. Stomachs of Ascidians, Belfast 
Lough, Co. Antrim. 
Navicula splendida, (Gregory). Marine. 
Valve large, deeply constricted; median compartment wide, 
greatly inflexed at the ends, greatly constricted in the middle; com- 
partments at either side narrow, having the inner edge milled; mar- 
ginal band of strie narrow in the middle, widening in a graceful curve 
towards the middle of the lobe, then narrowing towards the somewhat 
lanceolate ends; striz convergent in the middle, radiate towards the 
