258 Proceedings of the Royal Irish Acadetny. 



Smith does not figure the fine marginal striae, and describes the 

 marginal triangular bars as if they were monilif orm ; but with this 

 exception his figure is in every respect accurate, so as to remove all 

 doubt as to the identity of the species. Walker- Arnott considers that 

 Smith's form is identical with C. minutula, Kiitz., found by him in 

 the Liineburg deposit, and adds, "It is this which Smith obtained 

 from the Lough Mourne deposit, but which he has iinfortunately 

 referred to C. antiqua, a species which does not occur in any of the 

 Irish deposits which I have examined." On Cyclotella, Q. J. M. S., 

 Oct., 1860, p. 246. The forms of Cyclotella found on the only slide 

 I possess from the Liineburg deposit are those of C. operculata. 

 "Walker- Arnott evidently had not seen any specimen of C. antiqua, 

 for the distinctiveness of the species is too obvious to have escaped his 

 keen observation, had even a single form of it come under his notice. 



Wm. Sm., B. D., Vol. i., p. 28 ; PI. v., fig. 49. Ealfs, in Pritch., 

 p. 812. Kab. PL Eur., p. 33. 



Lough Mourne deposit, in which I have occasionally noticed it. 

 Sub-peat deposit, Dromore, Strangford Peat, Co. Down. 



Cyclotella rotula, (Kiitz.) Presh water. 



Yalve with a slight depression towards the centre, striae radiate, 

 running from the margin to the centre ; coarse at the margin, finer 

 and finer as they approach the centre, where they appear confused. 

 Striae linear, but notched, so as to seem moniliform. (PI. 26, 

 fig. 14.) 



In consequence of supposing that Discoplea rotula of Ehr., Mic, 

 T. XXXV. A. xxii., fig. 67, was a species of Cyclotella, Kiitzing, in his 

 Species Algarum, changed his original specific name to that of Cyclo- 

 tella astrsea, and this nomenclature has been adopted by Ralfs and 

 Rabenhorst. It is not, however, certain that Ehrenberg's form pro- 

 perly belongs to Cyclotella, and therefore the original name ought to 

 be retained. 



Kiitz. Bac, p. 50, T. ii., fig. 4. W. Sm., B. D., Yol. i. p. 28 ; 

 PI. v., fig. 50. Walker- Arnott, Q. J. M. S., Oct., 1860, p. 247.— Cy- 

 clotella astraea, Ralfs, in Pritch., p. 812. Ptab. PI. Eur., p. 34. — Or- 

 thosira rotula, Heiberg, De Danske Diat., p. 32. Cleve, Om Svenska 

 och JSTorska, Diat., p. 217. 



Lough ISTeagh, in several parts. Lucan, Peather-bed mountain, 

 and Grand Canal, Co. Dublin. River Bann, near Coleraine, Co. Derry. 

 Lough Mourne and Lough Island-Eeavey deposits. Small forms of 

 this species may be, at first view, readily mistaken for Cyclotella oper- 

 culata, but on close inspection the difference will be obvious. 



Cyclotella papulosa, (N. S.) Freshwater. 



Marginal striae of the valve linear, very fine, central portions 

 unstriate and occupied by a circlet of papillae, usually five or six in 

 number. (PL 26, fig. 15.) 



