376 Proceedings of the Royal Irish Academy. 



and distinguished by the apparent absence of striae." If the valve be 

 examined in a dry state, the longitudinal striae are distinct, but much 

 less numerous and distinct than in jN^avicula affinis ; the margin 

 also, instead of being perfectly linear as it is in the last named species, 

 is slightly elliptical. 



Lough Mask, near Tourmakeady, Co. Mayo. Featherbed Moun- 

 tain, Co. Dublin. 



Navicula rostellum, ("Wm. Sm.) Fresh water. 



Valves broadly elliptical ; ends produced into very short narrow 

 apices ; longitudinal sulci parallel to median line distinct ; striae 

 obscure; length -0020; breadth -0010. (Plate 31, fig. 53.) 



Wm. Sm., B. D., Vol. ii., p. 93. Ealfs, in Pritch., p. 900. Gru- 

 now, Verhancl. der K. K. Zool. Bot. Gesell., Band x., 1860, p. 550, 

 T. iv., fig. 10. This form, as described by Grunow, is narrower, and 

 the apices much wider than in my specimens ; the transverse striae as 

 described, are very fine and parallel, but as my specimens were mounted 

 in balsam, I could not detect the striae. Donkin, N. H. Brit. Diat., 

 p. 40, PL vi., fig. 7. Eab. Fl. Eur. Alg., sect, i., p. 195. The last 

 named author describes the striae as very delicate and parallel. — Navi- 

 cula apiculata, Gregory Q. J. M. S., Vol. iv., 1856, PI. i., fig. 13, who 

 attributes the form to Wm. Smith. 



Killakee, Co. Dublin. 



Navicula Icevissima, (Kiitz.) Fresh water. 



Valve colourless, slightly expanded in middle, slightly constricted 

 towards the broad rounded ends ; median line strongly developed ; 

 transverse striae very fine, slightly radiate ; longitudinal striae distinct ; 

 intermediate free space narrow, except in the middle, where some- 

 times it seems to expand in a short narrow stauroform band ; at the 

 extreme end a distinct transverse line is noticeable at right angles 

 with the median line ; length -0015, breadth -0004. (Plate 31, fig. 54.) 



Kiitz. Bac. p. 96, T. xxi., fig. 14. Wm. Sm., B. D., Vol. ii., 

 p. 91. Grunow, Verhand. der K. K., Zool. Bot. Gesell., Band x., 

 1860, p. 549, T. iv., fig. 5. Eab. Fl. Eur. Alg., sect, i., p. 188. 

 Donkin, N. H. Brit. Diat., p. 28, PI. v., fig. 2. 



Lower Lake, Killarney, Co. Kerry. Derrylane Lough, Co. Cavan. 

 Lough Neagh, near Antrim town. Ulster Canal, near Poyntzpass, 

 Co. Armagh. Loughbrickland Lake, Co. Down. Eiver Bann, near 

 Coleraine, Co. Derry. Trinity College Botanic Gardens, Co. Dublin. 

 Killeshin, Queen's Co. Feighcullen, Co. Kildare. 



Navicula oUongella, (Naegeli ?) Fresh water. 



Valve small, linear, elliptical ; ends rounded ; longitudinal sulci 

 close to median line, strongly developed, parallel ; transverse striae 



