306 Proceedings of the Royal Irish Academy. 



Var. longiceps, (Ehr.) Fresh water. 



Like the preceding, hut longer, more slender, the ends not so 

 large; not triangular, hut rounded off. (PI. 28, fig. 23.) 



Synedra longiceps, Eah. Siissw. Dial., p. 55. Ealfs, in Pritch., 

 p. 788. Grunow, Verhand. der K. K. Zool. Bot. Gesel. Band xii., 

 1862, p. 386. — Synedra notarisii, Castracane, Dialogo di Diat. raccolte 

 nell Yal. Intrasca, p. 9. 



Twyford Lough, near Athlone, Co. "Westmeath, unmixed with the 

 former, and mixed with it in ditch near railway station, Dundalk, Co. 

 Louth. 



Synedra uhia, (Ehr.) Fresh water. 



Frustules on front view linear ; on side view linear, suddenly con- 

 tracted at the ends, which are slightly constricted and rounded ; striae 

 interrupted in the centre hy a quadrangular vacant space. (PI. 28, 

 fig. 24.) 



It is not easy to comprehend how Smith could have regarded as 

 one species the two forms described by him under this name, B. D., 

 Vol. i., p. 71, PI. xi., figs. 90 and 90^, than which no two forms of 

 the genus seem to be more distinct. The result is, that great confu- 

 sion has been introduced, which may be dispelled by a careful com- 

 parison of Kiitzing's description and figure of the species with the 

 actual forms. It is questionable whether the form figured by Smith, 

 as above, fig. 90 ^, really belongs to Synedra ulna ; but, unqestion- 

 ably, that of fig. 90 must be excluded from its limits. 



Kiitz. Bac, p, 66, T. xxx., fig. 28. Bab. Siissw. Diat., p. 54, 

 T. iv., fig. 4. Ralfs, in Pritch., p. 788, PL x., fig. 184, in which only 

 the front view is given, and the mode of growth is on a short stipes, 

 and scattered. Grunow, Yerhand. der K. K. Zool. Bot., Gesel. Band 

 xii., 1862, p. 397, where he identifies this species with Smith's fig. 90^, 

 as above cited, and makes fig. 90 a variety marked by the name of 

 lanceolata. Heiberg refers to the species as identical with that of 

 Smith's fig. 90; DeDanskeDiat., p. 64. Eabenhorst Fl. Eur., sect. 1, 

 p. 133, does not refer to Smith's figures, and follows Grunow, only 

 that he includes Synedra salina, a very distinct species, as a variety of 

 Synedra ulna. Castracane identifies the form so named with that of 

 Babenhorst Siissw. Diat., T. iv., fig. 4, as well as with that of Smith, 

 fig. 90. Catalogo di Diat. raccolte nell Vail. Intrasca, p. 10. 



Tacumshane, Co. Wexford. Caum Lough, near Tralee, Glencar, 

 Co. Kerry. Biver Dodder, Co. Dublin. Ditch near Wicklow. Feigh- 

 cuUen, Maynooth, Co. Kildare. Biver Moy, Foxford, Co. Mayo. 

 Well, Farraghy, Co. Cork. 



Var. oxyrhyncTius, (Kiitz.) Fresh water. 



Much longer than the typical species, and ends on side view 

 sharper. (PI. 28, fig. 25.) 



Ktitz. Bac, p. 66, T. xiv., fig. 11. Ralfs, in Pritch., p. 788. 



