300 Proceedings of the Royal Irish Academy. 



Synedra acida, (Kiitz.) Fresli water. 



Fmstules long and very narrow ; on front "view attennated at tlie 

 ends ; on side riew narrow, attenuated towards the ends, wMch. are 

 usually expanded very slightly, but frequently acute. (PL 28, 



fig. 12.) 



Kiitz. Bac, p. 65, T. xiv., fig. 20. — Synedi-a delicatissima, ^m. 

 Sni., B.D., Yol. i., p. 72, PI. sii., fig. 94, who represents the striae as 

 inteiTupted in the middle by a distinct median line with small central 

 nodule, featm-es which do not exist. Ealfs, in Pritch, p. 787. Cas- 

 tracane, Catalogo di Diat. raccoltenell Yal. Intrasca, p. 10. — Synedra 

 acus, var. elongata, Gruuow, Yerhand. der K. K. Zool. Bot. Gesel., 

 Bandxii. 1862, p. 399. 



Tac'omshane, Co. Tv^exford. Stream, Crossdoney, Co. Cavan. 

 Friarstown, ITalahide, Well St. Penton's, Sutton, Co. Dublin. Hen- 

 derson's Well, Aughnacloy, Co. Tyrone. 



Var. tenuissima, (Kiitz.) Fresh water. 



In all respects like the typical species, except that it is smaller, 

 and much less attenuated at the ends on side view. 



Synedra tenera, YTm. Sm., B.D., Yol. ii., p. 98. Ptalfs, in 

 Pritch., p. 717, who makes the form described by Smith under this 

 name distinct fi'om Synedra tenuissima, with which I consider it is 

 identical. — Synecba acus, Gruuow, Yerhand. der K. K. Zool. Bot. 

 Gesel., Band xii., 1862, p. 398. 



"Lough Alloa, near Blarney, and near Kill aloe, Co. Cork," "\Ym. 

 Sm., Bohemabreena, Dundnim, Boat harbour. Dolphin's bam. 

 Eiver Dodder, St. Pent on' s Y^ell, Sutton, Stream, Blacki'ock, Co. 

 Dublin. Killeshin, Queen's County, Donoghmore, Co. Tyrone. 



Synedra gracilis, (Kiitz.) ilai'ine. 



Frustules small, '0012 in length; on front view attenuated 

 towards the ends ; on side view narrow, elliptical, broader in the middle, 

 gradually attenuated towards the rounded and slightly-expanded ends ; 

 stipes short, nearly sessile ; the fnistules being few and radiating 

 slightly. (PL 28, fig. 13.) 



Kiitz. Bac, p. 64, T. iii., fig. 14, T. xiv., fig. 2 I, T. xv., fig. 8, 

 1, 2, 5. Ptalfs, in Pritch., p. 786, regards tliis form of Kiitzing as iden- 

 tical with that so named by Wm. Smith, B. D., Yol. i., p. 70, PL xi., 

 fig. 85. The forms, however, axe quite distinct. Grunow, Yerhand. 

 der K. K. Zool. Bot. Gesel., Band xii., 1862, p. 401. It is to be re- 

 marked that the last-named author regards this species and Synedi'a 

 barbatula, Kiitz. Bac, p. 68, T. xv., fig. 10, as so nearly allied that 

 the latter is to be regarded merely as a variety of the former. I can- 

 not adopt this view, and for these reasons : fii'st, the gi'owth of the 

 two is quite distinct ; the fi-ustules in Syncdi-a barbatula are attached 

 in tablets, while those of Synedi'a gi'acilis are fewer in number, and 



