O'Meara — Bejwrt on the Irish JDiatoniacece. 307 



Oruno'w makes Synedra oxyT}iyiich.us a distinct species, whicli lie iden- 

 tifies with Synedra oxyi-liynchus, Wm. Sm., B. D., Yol. i., p. 71, 

 PI. xi., fig. 91, and figiu'es a variety distinguished as amphicephala, 

 which appears identical with Synedi-a ulna, Wni. Sm., B. D., Vol. i., 

 p. 71, PI. xi., fig. 90 i?. The form xxnder consideration seems diffe- 

 rent from both. Bah. PI. Eui'., sect. 1, p. 135, who follows Grunow. 



Hiver Dodder, near Dublin. Eiver AToy, Foxford, Co. Mayo. 



Var. amphirhyncJius. Ehr. Fresh water. 



Like the typical species, fi'om which it differs chiefly by the ab- 

 sence of the quadrangular unstiiate space in the centre of the valve, 

 on side view. (PI. 28, fig. 26.) 



Kiitz. Bac, p. 66, T. xiv., fig. 15. Bab. Siissw. Diat., p. 55, 

 T. iv., fig. 7. Balfs, iuPritch., p. 788. Grunow, Yerhand. der K.K, 

 Zool. Bot., GeseL, Band xii., 1862, p. 397. 



Eiver Moy, Foxford, Co. Mayo. Bohernabreena, Biver Dodder, 

 3)ond, Botanic Gardens of Trinity College, Co. Dublin. Greenane, 

 Eilcool, Powerscoiu-t, Co. "Wicklow. Feighcnllen, Co. Kildare. Kille- 

 shin. Queen's County. Well, Farraghy, Co. Cork. Stream near Giants' 

 Causeway, Co. Antrim. 



Mr. Kitton of IS'orwich, and Bev. George Davidson, have supplied 

 me with specimens which would appear to belong to this variety, but 

 growing in short filaments, after the manner characteristic of Fragi- 

 laria. I find no description of the stipes in any of the authors who 

 liave referred to this form, nor have I ever seen it myseK in situ; but 

 not unfi-equently have I noticed it aggTegated in tablets, but not 

 parallel at the ends, as if the aggregation were accidental. 



Synedra longisdma, (Wm. Sm.) Fresh water. 



Frustules very long on front view, quadrangular ; on side view li- 

 near, till near the ends, towards which it is almost imperceptibly 

 attenuated ; ends constricted and then dilated, without any central 

 free space; valves sometimes slightly arcuate. (PI. 28, fig. 27.) 



Smith's description of this species is tolerably accurate ; but the 

 ^figure, B.D., Yol. i., PI. xii., fig. 95, is calculated to mislead. The 

 form possesses no median line, nor is there a central fi'ee space, such 

 as this figure represents. 



Wm. Sm., B. D., Yol. i., p. 72. Balfs, in Pritch., p. 786, who 

 asks "is this distinct from Synedi-a biceps?" to which I reply, cer- 

 tainly it is. The forms differ greatly in their general appearance, 

 and may be discriminated by the fact that the strife in Synedi-a bi- 

 ceps are pervious — in Synedra longissima they are separated by a 

 median sulcus. Cleve, Om Svenska och Norska Diat., 220. Bab. 

 Fl. Eur., sect 1, p. 130, who remarks that "it appears to him an 

 elongated, gently-undulate form of Synedra biceps," and strangely 



