280 Proceedings of the Royal Irish Academy. 
p.. 52, Pl, xlvu. - Ralis, an Pritch., p. 58h. . Rab; FL. Eurs;sect. 1, 
p. 309. 
This and the following species have been described by different 
authors under different generic and specific names, e. g., Isthmia obli- 
quata, Ag. ; Diatoma obliquatum, Lyng.; Isthmia obliquata tenuior, 
Ag.; Conferva obliquata, Engl. Bot., tab. 1869; but as it is not 
certain in all cases which of the two species was intended, it seems 
better not to attempt further identification. 
Collected in great abundance by Dr. D. Moore on Polysiphonia in 
Camlough Bay, Co. Antrim; and found by me in almost every marine 
gathering from that place northwards, but not at all m the same pro- 
fusion. Malahide, Co. Dublin. 
Isthmia enervis, (Ehr.) Marine. 
Striation of valves areolate, areoles quadrangular ; without coste-; 
areoles on connecting membrane much smaller, and roundish. 
The frustules are generally slighter than in the former species, 
but the distinctive characters are, first, the absence of the costae, and 
secondly, the want of a distinct border on the valve in side view, so 
conspicuous in Isthmia nervosa. 
Kutz. Bac,, p. 1o7,. 0. xix. fie. 4. Win: oma 107 een a me 
p 42, Pl. xivin. . Ralfs,.in Prteh, ps 851, Bl. x., fig. 193. Rab- 
Fl. Eur., sect. 1, p. 309. 
Stomachs of Ascidians, Roundstone Bay. Arran Islands, Co. 
Galway. Malahide, Co. Dublin. 
Famiry V. FRAGILARIEA, Kitz. 
Frustules in front view rectangular, without median line, central 
nodule, or internal diaphragms. The frustules are usually attached 
by a stipes, or united together in parallel or zig-zag filaments. 
The group thus limited embraces the following genera :—Fragi- 
laria, Denticula, Odontidium, Plagiogramma, Dimeregramma, Diatoma, 
Synedra, Raphoneis, and is tolerably well defined by the common 
characteristics above specified. In the case of Raphoneis indeed it is 
doubtful whether the frustules are free or stipitate. I have never seen 
them in a growing state, but in other respects they exhibit the com- 
mon character of the Fragilariee. 
The above genera have been distributed by different authors. 
very differently from their present arrangement. Kiitzing grouped 
such of the above genera as were known to him under the Fragilarie, 
with the exception of Synedra, which he and others have unaccount- 
ably, as it appears to me, placed under the Surirellee. William 
Smith, who attaches great importance to what others have regarded as. 
