296 Proceedings of the Royal Irish Academy. 



Rhaphoneis lorenziana, (GrunoTv.) Marine. 



Yalves considerably larger than the last named, and in all respects 

 similar, except that in outline the valves are rhomboid. 



Grrunow, Verhand, der K. K. Zool. Bot. Gesel., Band xii., 1862, p. 

 381, T. iv., fig. 5. 



Piles of wooden bridge, DoUymonnt, Co. Dublin. 



Rhwphoneis lilurnica, (Grunow.) Marine. 



Yalves broadly elliptical, almost circular ; striae large, monilif orm, 

 squarish, distinct, larger at the middle, and decreasing in size as they 

 approach the margin, radiate ; median unstriate, space narrow, ellipti- 

 cal. (PL 28, fig. 5.) 



This form presents very much the appearance of a Cocconeis, in 

 which genus I would have provisionally placed it, were it not that 

 Grunow, who first discovered it, placed it here. 



Grunow, Verhand der Zool. Bot. Gesel,, Band xii., 1862, p. 383, T. 

 iv., fig. 6. 



Arran Islands, Co. Galway. 



Rhaphoneis Sarrisonii, (Wm. Sm.) Presh water. 



Prustules attached, filamentous, connected by their ends ; on front 

 view quadrangular; on side view somewhat cruciform ; angles rounded; 

 striae costate, slightly radiate ; median unstriate space narrow, linear. 



OdontidiumHarrisonii, "Wm. Sm., B. D., Yol. ii., p. 18, Supp. PI. Ix., 

 fig. 373. — Dimeregramma Harrisonii, Ealfs, in Pritch., p. 290, PL viii., 

 fig. 6. — Pragilaria Harrisonii, Eab. PL Eur., sect. 1, p. 119. — Diatoma 

 Hanisonii, Cleve, Om Svenska och JSTorska Diat., p. 219. 



Priarstown, Xillikee, PJver Dodder, Bohernabreena, Co. Dublin. 

 Hoyal Canal, near Enfield, Co. Kildare. Portadown. Yerner's 

 Bridge, Co. Armagh. 



Genus IX. Stnedea, Ehr. 



Prustules long and narrow, both on side and front view ; attached 

 by a gelatinous cushion, or by a longer or shorter stipes. 



The characteristics of this genus are so well marked, that very little 

 difference of opinion has existed from the first as to the grouping of 

 the several species, although the relation of the genus to other genera 

 has been very differently represented. Kiitzing includes Synedra in 

 his group of Surirellese, in which besides he ranges the genera Campylo- 

 discus, Surirella, and Bacillaria. The last named has, indeed, a super- 

 ficial resemblance to the frustules of Synedra, but, in consequence of 

 its unsymmetrical character, has, by more recent authors, been trans- 



