280 Proceedings of the Royal Irish Academy. 



p. 52, PL xlvii. Ealfs, in Pritch., p. 581. Putb. PI. Eiix., 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- 

 qnata, Ag. ; Diatoma obliquatum, Lyng. ; Isthmia obliqnata tenuior, 

 Ag. ; Conferva obliqnata, Engl. Bot., tab. 1869 ; bnt as it is not 

 certain in all cases which of the two species was intended, it secms- 

 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 in the same pro- 

 fusion. Malahide, Co. Dublin. 



Isthmia enervis, (Ehr.) Utlarine. 



Striation of valves areolate, areoles quadrangular; without costa3 j. 

 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 co stse, and. 

 secondly, the want of a distinct border on the valve in side view, so 

 conspicuous in Isthmia nervosa. 



Kiitz. Bac, p. 137, T. six., fig. 4. Wm. Sm., B. D., Yol. ii.^ 

 p. 52, PL xlviii. EaKs, in Pritch., p. 851, PL x., fig. 183. Eab. 

 PL Eur., sect. 1, p. 309. 



Stomachs of Ascidians, Poundstone Bay. Arran Islands, Co.. 

 Galway. Malahide, Co. Dublin. 



Eamilt Y. PEAGILAEIE^, Kiitz. 



Prustules in front view rectangular, without median line, central 

 nodule, or internal diaphragms. The fi'ustules are usually attached 

 by a stipes, or united together in parallel or zig-zag filaments. 



The group thus limited embraces the following genera : — Pragi- 

 laria, Denticula, Odontidium, Plagiogramma, Dimeregramma, Diatoma, 

 Synedra, Eaphoneis, and is tolerably well defined by the common 

 characteristics above specified. In the case of Eaphoneis 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 Pragilarieae. 



The above genera have been distributed by different authors- 

 very differently fi'om theii' present arrangement. Kiitzing grouped 

 such of the above genera as were known to him under the Pragilariese, 

 with the exception of Synedra, which he and others have unaccount- 

 ably, as it appears to me, placed under the Surirellese. "William 

 Smith, who attaches great importance to what others have regarded as. 



