O'Meara — RepoH on the Irish Diatomacece. 291 



Genus YI. Diatoiia, De CandoUe. 



Frustules united in zig-zag filaments ; strongly costate ; costse per- 

 vious. 



Grunow states tliat the various species of this genus, as well as 

 those of Odontidium, possess fine striae intei'posed hetween the costse, 

 although in the former they are more difficult to he discovered than in 

 the latter. The most careful examination of the valves of Diatoma, 

 on my part, has, as yet, failed to hring them out. 



Diatoma vidgare, (Bory.) Fresh water. 



Yalves miich arched, so that the costse present a deep margin on 

 the front view ; on side view the outline is elliptical, sometimes nar- 

 rowed towards the ends ; costae strong and close. 



Kiitz. Bac, p. 47, T. xvii., fig. 15, 1-4. Eah. Siissw. Diat,, 

 p. 35, T. ii., fig. 6. Wm. Sm., B. D., Vol. ii., p. 39, PI. xl., fig. 309. 

 RaKs, in Pritch., p. 778, PI. iv., fig. 13, PI. ix., fig. 168. Grunow, 

 Yerhand der K. K. Zool. Bot. Gesel., Band xii., 1862, p. 363. Hei- 

 herg, De Danske Diat., p. 57. Cleve, Om Svenska och Norska Diat., 

 p. 219. Castracane, Catalogo di Diat, raccolte nell Yal Intrasca, 

 p. 15. 



River Dodder, Grand Canal at Portobello, Co. Duhlin. "Well, 

 Strokestown, Co. Roscommon. Stream in Glebe, Delgany, Co. "Wick- 

 low. River !Moy, Poxford, Co. Mayo. Stream, Ealleshin, Queen's 

 County. River Lee, Co. Cork. 



Diatoma grande, (Wm. Sm.) Presh water. 



Prustules on front view slightly inflexed; on side view linear, 

 slightly constricted towards the capitate ends; costse fine, close. (PL 

 28, fig. 1.) 



Wm. Sm., B. D., YoLii., p. 39, PL xl., fig. 310. Ralfs, in Pritch., 

 p. 779. Heiherg, De Danske Diat., p. 57. Castracane, Catalogo di 

 Diat. raccolte nell Yal Intrasca, p. 15. — Diatoma vulgare var. grande. 

 Grunow, Yerhand der K. K. Zool. Bot. Gesel., xii., Band 1862, p. 

 364. — Diatoma Ehrenhergii fonoia grandis, Rab. PL Eur., sect. 1, 

 p. 122. Grunow stands alone in subordinating this form to Diatoma 

 vulgare, fi'om which it stands distinguished by numerous characters : 

 so distract is it from that species in the outline of the valve, both in 

 front and side view, that it seems deserving of occupying the place of 

 a separate species. 



River at Belleek, Co. Permanagh. Tacumshane, River Slaney, 

 near Killurin, Co. Wexford. River Shannon, near Athlone, Co. Ros- 

 common. Lough Corrib, Co. Mayo. Lough Derg, Co. Galway. 

 Lough Neagh, Co. Armagh. Killikce, River Liffey, Co. Dublin. 



