400 Proceedings of the Royal Irish Academy. 
tinct species, and named Navicula donkinii, the name which I had 
given to it in my list before the Atlas had come under my notice. 
The form here described agrees precisely with Gregory’s description of 
Nayicula musca, which may readily be distinguished from Navicula 
donkinii, by its much deeper constriction, and the sharp outline at the 
ends, in consequence of which it resembles the abdomen of a fly; 
the strie, too, in this are punctate, while in the other they are 
costate. 
Piles of wooden bridge on Dollymount Strand, Co. Dublin. 
Navicula interrupta, (Kiitzing). Marine. 
Valve deeply constricted; lobes suborbicular; median compart- 
ment broad, greatly inflexed ‘at the ends, considerably constricted in 
the middle ; compartments on either side very narrow, bilunate,. 
unstriate ; marginal band of strie very narrow in the middle, where 
the strize seem to fail, but tolerably wide in the middle of the lobes ; 
strize costate, nearly parallel in the middle, radiate towards the ends; 
length ‘0023, breadth, -0010 ; at constriction -0007. (Plate 33, fig. 26.) 
Kutz. Bac... p.t00, PT. xxtx,, “fe. Oo... Sealiay mi tecte bh eagerees 
Rab. Fi. Hur. Alo. sect.7.; p. 200. Donlan, No Bat wists yar 
Pl. vi., fig. 2. . Schmidt, Atlas, T. xii., fig. 2—Navicula didyma, 
Win. Sm:, B.D... Volsa.:9. 60,5). xum. sie naa, 
Ballysodare, Co. Sligo. Lough Gill, Co. Kerry. Arran Islands ; 
Stomachs of Ascidians, Roundstone Bay ; Stomachs of Ascidians, 
Broadhaven Bay, Co. Galway. Seaweeds, coast of Co. Clare. 
Navicula apis, (Ehr.) Marine. 
Valve deeply constricted, ends narrowed and rounded; median 
compartment broad, with well-defined boundary lines, shghtly inflexed 
at ends, slightly constricted in the middle; compartments at either 
side unstriate, narrow, tapering to a point at the ends; marginal 
band of strize narrow in the middle, increasing considerably, and then 
narrowing towards the ends; strie in the middle apparently costate, 
convergent towards the ends, radiate, and having the appearance more 
of fine coste interrupted by close longitudinal sulci, than of being 
moniliform; length 0038, breadth -OO11; pHa a the constric- 
tion 0008. (Plate 33, fig. 27.) 
There is great difficulty i in identifying the species so named, and 
with some hesitation have I come to my conclusion on the subject. 
Kiitzing’s figure of Navicula apis is shorter and stouter than the pre- 
sent, and the striz are so indistinct as to furnish no help. Donkin’s 
figure in outline is precisely the same as in the form under considera- 
tion; the striae, however, are represented as more decidedly punctate, 
and the compartments on either side of the median one are distinctly 
striate. Inthe present case, there is sometimes an appearance of striae 
