286 Proceedings of the Royal Irish Academy, 



Smith, -with doubtfulness, refers Diatoma tenue, Kiitz. Bac, p. 48, 

 T. xviii., 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 xii., 1862, 

 p. 362. As so 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, Bohemabreena, Co. Dublin. Connemara, Co. Galway. Black 

 Castle, Glenchree, Co. "Wicklow. Peighcullen, Royal Canal, near En- 

 field, Co. Kildare. Tacumshane, Co. "Wexford. Killeshin, Queen's 

 County. 



Genus III. Odontidium, Kiitz. 



Frustules united in longer or shorter parallel filaments ; on front 

 view regularly rectangular, on side view elliptical, costate ; costse 

 pervious; their ends very conspicuous on front view. 



Odontidium sinuatum, (Wm. Sm.) Presh water. 



Frustules united in short filaments ; on side view somewhat lanceo- 

 late ; outline sinuous ; expanded and angular in the middle ; costse 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 Mtzschiese ; and Habenhorst, 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 costse. 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 costse from one side to 

 the other, and at the extremities, where the convexity appears less 

 than in the middle, the persistent character of the costse is easily 

 traced. 



Denticula sinuata, "Wm. Sm., B.D., Vol. ii., p. 21, PI. xxxiv., 

 fig. 295. Castracane, Catalogo di Diat. raccolte nell Val Intrasca, p. 14. 

 — Dimeregramma sinuatum, Ealfs, in Pritch., p. 730, PL iv., fig. 12. 



River Dodder, Co. Dublin. Slate quarry, Glanmore, Co. "Wicklow. 

 Lough Gill, Co. Kerry. 



