328 Proceedings of the Royal Irish Academy. 
bability, this is identical with the form described by Greville, Q.J.M.S., 
October, 1862, p. 235, Pl. x., fig. 11; although that author remarks 
that in his form the striae were much more obscure than in the form 
figured by Smith as above. 
_ Lough Corrib, Co. Galway, mixed with the typical form. 
Mastogloia grevillii, (Wm. Sm.) Fresh water. 
Valve linear; cuneate at the obtuse extremities; marginal plate 
nearly linear on the inner margin, suddenly attenuated towards the 
ends; loculi numerous; strie fine, linear, radiate, shortened at the 
central nodule, so as to give a stauro-form appearance to the valve. 
Wm. .Sm. B. D. Vol. u.,. p..64, Supp. Pl. lxu, fig. 389. Ralfs, im 
Pritch., p. 925. Grunow, Verhand. der K. K. Zool. Bot. Gesel., 
Band x., 1860, p. 575. Heiberg, De Danske Diat., p. 94. Rab. FI. 
Eur., sect. 1, p. 260. 
Kileool, Co. Wicklow. Lough Neagh, Co. Antrim. Ballyshannon, 
Co. Donegal. Carrickhugh, Co. Derry. 
Mastogloia costata, N.S. Fresh water. 
Valve linear; cuneate at ends; length ‘00138, breadth :0005 ; mar- 
ginal plates broad, on inner margin perfectly linear till near the ends, 
where they very slightly expand, in shape of a spear head; loculi 
numerous; striz strongly costate, converging in the middle, and for 
the rest radiate ; shortened at the central nodule. (Pl. 29, fig. 13.) 
In shape and size, this form is so like Mastogloia grevillii that it 
might easily be confounded with it; but, however, on closer investi- 
gation it will appear quite distinct. In M. grevillii, the fine linear 
strie can by proper focusing be easily seen along with the loculi of 
the marginal plate. In the present species, either from the convexity 
of the valve, or the coarseness and closeness of the costate strie, or 
perhaps owing to both these circumstances, the plates are not easily 
detected, except at the inner margin, where their boundary may be 
detected by the clear intervening space into which the ends of the 
strong coste are seen to project. 
On a moist rock, Ballyshannon, Co. Donegal. 
Genus II. Dicxzera, Berkeley. 
Frond flat, leaf-like ; unbranched; frustules scattered without re- 
gular arrangement. 
———————_—. 
Smith attributes this genus to Ralfs; but Ralfs himself ascribes it 
to Berkeley. It is adopted by Kiitzing, Smith, Grunow, and Raben- 
