O’Meara—Report on the Irish Diatomacee. 403 
ends, moniliform, the beads being quadrangular; length -0040, 
breadth -0012; breadth at the constriction ‘0007. (Plate 33, fig. 30.) 
Gregory, Q. J. M.-S,, 1856, Pl. v., fig. 14... Ralfs, in Pritch., 
p. 893. Rab. Fl. Eur. Alg., sect. 1., p. 204.— Navicula entomon. 
Donkin, N. H. Brit. Diat., p. 49, Pl. vii., fig. 5. The outline of this 
form greatly resembles that of Navicula incurvata, which Rabenhorst 
makes a variety of this species. So different, however, is the character 
of the strie, that they cannot properly be considered as nearly related. 
The present form differs so much, both in outline and striation, from 
Navicula entomon, that it ought to be considered a very distinct 
species, 
Arran Islands, Co. Galway. 
Navicula gregorit, (O’Meara). Marine. 
Valves considerably constricted, lobes much expanded, median 
compartment wide, greatly inflexed at the ends, slightly constricted 
in the middle; central nodule large, quadrangular, with three short 
spine-like projections at each side ; compartments on either side nar- 
row, attenuated to a point at the ends, roundly expanded in the mid- 
dle; marginal band of strie wide; strize convergent in the middle, 
radiate towards the ends, moniliform; beads large, quadrangular ; 
length ‘0045, breadth :0028; breadth at the constriction ‘0016. 
(Plate 33, fig. 31.) 
Navicula didyma, var. y. Gregory, Q. J. M.8., 1856, p. 45, 
PE Vs. ne: 16. 
Arran Islands, Stomachs of Ascidians, Roundstone Bay, Co. 
Galway. 
Navicula williamsonii, (Wm. Sm.) Marine. 
Valvelarge ; margin incurved, rather than constricted ; median com- 
partment wide, inflexed at the ends, constricted in the middle; com- 
partments at either side scarcely so wide as the median one, narrowed 
to a point at the ends, greatly expanded, and anglewise in the mid- 
dle, striate; marginal band of strie wide; striz slightly convergent 
in the middle, radiate towards the ends, moniliform; beads large, 
quadrangular; length 0072, breadth 0029; breadth at the middle 
-0026. (Plate 33, fig. 32.) 
Navicula didyma, sporangial var.? Wm. Sm., B. D., Vol. i, 
p- 58, Pl. xvu., fig. 154*—Navicula smithu, Donkin, N. H. Brit. 
Diat., p. 6, Pl.1., fig. 4. This form on first view would appear to be 
an incurved variety of Navicula fusca, which it resembles much more 
than it does Navicula smithiu. I believe it is only necessary to see 
the form, which is extremely rare, in order to be convinced that it is 
as distinct from Navicula didyma as it is from Navicula fusca. Pro- 
fessor Smith informs us that the species came under his observation 
in a collection made by Professor Williamson in the Isle of Skye. 
Arran Islands ; Stomachs of Ascidians, Roundstone Bay, Co. Galway. 
