286 Proceedings of the Royal Irish Academy. 
Smith, with doubtfulness, refers Diatoma tenue, Kiitz. Bac., p. 48, 
T. xviti., figs. 9, 10, and Odontidium striolatum, Kiitz. Bac., p. 45, 
T. xxi., fig. 20, to this species; and Grunow, under Diatoma tenue, 
Kiitz., remarks, ‘‘ I do not find this variety described in Wm. Smith’s 
Brit. Diat.,”? Verhand der K. K. Zool. Bot., Gesel., Band xu., 1862, 
p- 862. Asso much doubt rests upon the forms described by Kiitz- 
ing, I have referred the species to Wm. Sm., whose accurate figure 
removes all doubt as to the identification of it. 
Lough Mourne deposit. Ditch near Giants’ Causeway, Ballyleg, 
Co. Antrim. Derrylane Lough, Stream near Crossdoney, Co. Cavan. 
Lucan, Bohernabreena, Co. Dublin. Connemara, Co. Galway. Black 
Castle, Glenchree, Co. Wicklow. Feighcullen, Royal Canal, near En- 
field, Co. Kildare. 'Tacumshane, Co. Wexford. Kulleshin, Queen’s 
County. 
Genus III. Opontipium, Kiitz. 
Frustules united in longer or shorter parallel filaments; on front 
view regularly rectangular, on side view elliptical, costate; cost 
pervious; their ends very conspicuous on front view. 
Odontidium sinuatum, (Wm. Sm.) Fresh water. 
Frustules united in short filaments ; on side view somewhat lanceo- 
late ; outline sinuous ; expanded and angular in the middle; costz rela- 
tively fine. 
In consequence of the supposed excentric structure of the frustule 
of this species, Grunow has transferred the genus Denticula, as before 
stated, to the group Nitzschiee ; and Rabenhorst, taking the same view 
of the structure of the frustule, adopts his suggestion, but establishes 
a special genus, Grunowia, for its reception, a course in which he is 
followed by Cleve. This treatment appears to me inadmissible, inas- 
much as the frustules are, in general structure, perfectly symmetri- 
cal. In some specimens the striation appears on one side, while the 
opposite side seems destitute of costa. This may be an illusory appear- 
ance, arising from the convexity of the valve when viewed at an angle 
to the plane of the field; but, certainly, it is by no means universal. 
By accurate adjustment I have traced the costae from one side to 
the other, and at the extremities, where the convexity appears less 
than in the middle, the persistent character of the costze is easily 
traced. 
Denticula’ smuata, Wm. Sm.,. B.D., Vol. a1, p. 21, Pixar... 
fig. 295. Castracane, Catalogo di Diat. raccolte nell Val Intrasca, p. 14. 
—Dimeregramma sinuatum, Ralfs, in Pritch., p. 730, Pl. iv., fig. 12. 
River Dodder, Co. Dublin. Slate quarry, Glanmore, Co. Wicklow. 
Lough Gill, Co. Kerry. 
