O'Meara — Beport on the Irish Diatomaccce. 303 



lo be discriminated on the ground of habitat from Syn. pulchella. 

 Speaking of this last named fonn, Grunow sagaciously remarks, 

 "Whether this species is actually distinct from the preceding (Syn. 

 fasciculata, Grun. = to Syn. gracilis, Wm. Sm.), admits of considerable 

 doubt. Single frustules are not distinguishable. The separation is 

 founded only on the union in larger fans upon a stipes often tolerably 

 thick, which is by no means constant, and the occurrence in fresh 

 water." Yerhand der K. K. Zool. Bot. Gesel., Band xii., 1862, 

 p. 392. I am disposed to regard all these various forms as merely 

 Tarieties cf Syn. pulchella — and for this reason, that I have noticed 

 them more or less mixed together in gatherings from fresh water 

 localities, as well as in places where the water was slightly brackish, 

 .and almost always exhibiting features of mutual relationship. 



Synedra pulclielJa, (Kiitz.) Presh water. 



On fi'ont view linear, slightly attenuated towards the ends ; on 

 side view narrow, lanceolate, slightly capitate ; the median ring- 

 strongly marked. (PI. 28, fig. 17.) 



I have never seen the median ring so round or so decided in its 

 character as appears in Smith's figure of the species. 



Kiitz. Bac, p. 68, T. xxix., fig. 87. Wm. Sm., B. D., Yol. i., 

 p. 70, PL xi., fig. 84, Supp., PI. xxx., fig. 84. Eab. Siissw. Diat., 

 ,p. 56, T.iv., fig. 17. Palis, in Pritch., p. 786. Grunow, Yerhand. der 

 K. K. Zool. Bot. Gesel., Band xii., 1872, p. 392. Heiberg, De Danskc 

 Diat., p. 65, who considers it a brackish water form. 



Piver Erne, Crossdoney, Co. Cavan. Caum Lough, near Tralec. 

 Pedler's Lake, Dingle, Co. Kerry. Kilcool, Co. "Wicklow. Stream, 

 Piatragh, Co. Donegal. 



Var. gracilis, ("Wm. Sm.) Fresh water. 



This variety differs from the preceding only in not being con- 

 stricted at the ends, and the stipes being short, the frustules scattered 

 and not arranged in the form of a fan. In identifying this species we 

 can go no further back than the date of Smith's work, in which it is 

 faithfully delineated. Kiitzing's figures of the species named Syn. 

 gracilis are so indistinct that it would be impossible to identify them 

 with certainty. (PL 28, fig. 18.) 



Synedra gracilis, "Wm. Sm., B. D,, Yol. i., p. 70, PL xi., fig. 85. 

 Palfs, in Pritch., p. 786, who describes the form as marine. Eab. 

 PL Eui\, sect. 1, p. 132, where the form is stated to be submarine, in 

 which the author coincides with Smith. — Synedra fasciculata, Kiitz. 

 — Synedra saxonica, Kiitz, according to Grunow, Yerhand. der K. K. 

 Zool. Bot. Gesel., Band xii., p. 391. Cleve regards this species as 

 incidental to brackish water, and with Grunow considers it identical 

 with Synedi'a fasciculata, Kiitz, Om Svenska och KorskaDiat., p. 220. 



Stream, Port-na-Crush, Co. Donegal. Carnlough, Co. Antrim. 



