300 Proceedings of the Royal Irish Academy. - 
Synedra acula, (Kitz.) Fresh water. 
Frustules long and very narrow; on front view attenuated at the 
ends; on side view narrow, attenuated towards the ends, which are 
usually ‘ial very slightly, but frequently acute. (Pl. 28, 
fig. 12. 
Kiitz. Bac., p. 65, T. xiv., fig. 20.—Synedra delicatissima, Wm. 
Sm., B. D., Vol. i., p. 72, Pl. xii., fig. 94, who represents the striz as 
interrupted in the middle by a distinct median line with small central 
nodule, features which do not exist. MRalfs, in Pritch, p. 787. Cas- 
tracane, Catalogo di Diat. raccolte nell Val. Intrasca, p. 10.—Synedra 
acus, var. elongata, Grunow, Verhand. der K. K. Zool. Bot. Gesel., 
Band xii. 1862, p. 399. 
Tacumshane, Co. Wexford. Stream, Crossdoney, Co. Cavan. 
Friarstown, Malahide, Well St. Fenton’s, Sutton, Co. Dublin. Hen- 
derson’s Well, Aughnacloy, Co. Tyrone. 
ar. 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, Wm. Sm., B.D., Vol. u.,.p. 98. Ralfs, in 
Pritch., p. 717, who makes the form described by Smith under this 
name distinct from Synedra tenuissima, with which I consider it is 
identical Synedra acus, Grunow, Verhand. der K. K. Zool. Bot. 
Gesel., Band xi., 1862, p. 398. 
‘‘Tough Alloa, near Blarney, and near Killaloe, Co. Cork,’”? Wm. 
Sm., Bohernabreena, Dundrum, Boat harbour, Dolphin’s barn. 
River Dodder, St. Fenton’s Well, Sutton, Stream, Blackrock, Co. 
Dublin. Killeshin, Queen’s County, Donoghmore, Co. Tyrone. 
Synedra gracilis, (Kiitz.) Marine. 
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 frustules being few and radiating 
slightly. (Pl. 28, fig. 13.) 
Kiubz:, Bac.,:p.,64, heise tie 1a DE scl. 5 chee Da ee eae GO ae 
1,2, 5. Ralfs, in Pritch., p. 786, regards this form of Kiitzing as iden- 
tical with that so named by Wm. Smith, B.D., Vol. 1., p. 70, Pl. xi., 
fig. 85. The forms, however, are quite distinct. Grunow, Verhand. 
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 Synedra 
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: first, the growth of the 
two is quite distinct; the frustules in Synedra barbatula are attached 
in tablets, while those of Synedra gracilis are fewer in number, and 
