PARACYCLAS DTI NOYERI. 163 



Paeacyclas. dtj Noykri, Porthole, sp., 1843. Plate XXII, fig. 9. 



Litcina du Noyeri, Portlock, 1843. Rep. Greol. Londonderry, p. 571, pi. xxxviii, 



fig. 12, 



— antiqua, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 53, pi. viii, 



fig. 9. 



Specific Characters. — Shell of medium size, sub-orbicular, very moderately 

 gibbose. The margin is one unbroken curve from the anterior end of the hinge- 

 line to the posterior, the curvature varying somewhat in convexity. The hinge-line 

 is not very long and is arcuate. The umbones are sub-central, pointed, somewhat 

 elevated. The lunule is well marked. 



Interior. — Not exposed. 



Exterior. — The surface is ornamented with regular, fine, concentric lines of 

 growth, more pronounced on the anterior side of the valve. 



Dimensions. — PI. XXII, fig. 9, the type specimen, measures — 



Antero-posteriorly . . . .43 mm. 



Dorso-ventrally . . . .42 mm. 



From side to side (estimated from a single valve) . 8 mm. 



Localities. — Carboniferous Shales near Pettigo and Ballintrillick, Bundoran, 

 co. Donegal. 



Observations. — The type of Lucina Du Noyeri, Portlock, a right valve, is preserved 

 in the Collection of the Geological Survey Museum, Jermyn Street. It seems to me 

 that this specimen has been flattened by pressure, and consequently the umbo is 

 more pointed and raised than would have been the case normally. The type 

 specimen of Lucina antiqua, M'Coy, is in the Griffith Collection, Science and Art 

 Museum, Dublin, but the upper portion of the shell has disappeared. Judging from 

 the figure and description, I think there can be little doubt that M'Coy 's shell was 

 identifiable with Portlock's species. M'Coy's description is as follows : " Orbicular, 

 slightly convex, beaks pointed ; lunule very small ; surface marked with delicate, 

 sharp, concentric stria?." This is a perfect description of the type of L. Du Noyeri, 

 Portlock. With regard to the exact horizon at which this species occurs, Portlock 

 says (op. supra cit., p. 571) that " ascending geologically from the Old Red Sand- 

 stone, a buff-coloured grit commences the formation, which gives way to shales, 

 with impressions of plants. The shales are at first broken by alternating beds of 

 grit and then by beds of Limestone, possessing characteristic fossils of the true 

 Mountain Limestone, such as Producta comoid.es (Phill.), and then increasing in 

 magnitude, terminating upwards in the Pettigo Limestone. It is remarkable that 

 in this aggregate of highly calcareous shales the characteristic Modiola beds do not 



