AVICULOPECTBN PLICATUS. 73 



impossible to recognise the species ; and there is no wonder that very different 

 shells have hitherto been referred to Phillips's species in different collect inns. 



Aviculopecten plicatus, Sowerby, sp., 1823. Plate XII, fig-s. 5, 6, 8, 9. 



Pecten plicatus, Sowerby, 1823. Min. Conch., vol. iv, pi. dlxxiv, fig. 3. 

 Non — — Phillips, 1836. Geol. Yorks , pt. ii, p. 212, pi. vi, fig. 21. 



— — M'Coy, 1814. Synops. Carb. Foss. Ireland, p. 98. 



hians, M'Coy, 1844. Ibid., p. t»4, pi. xvi, fig. 6. 

 micropterus, M'Coy, 18 14. Ibid., p. 96, pi. xv, fig. 12. 

 Avicula plicata, Broivn, 1849. Illust. Foss. Conch., p. 160, pi. lxv, fig. 8. 



Specific ('Intruder*.- — Shell of medium size, fan-shaped, the body of the valve 

 triangularly ovate, the left valve only moderately convex, the right still less so. 

 The lower margin broadly convex ; the posterior margin sinuously curved, due 

 to the falcate posterior ear. The anterior ear smaller, triangular, depressed ; the 

 posterior ear large, its upper border extended and pointed, marked off from the 

 valve by an oblique sulcus, the lower part slightly convex, the upper flattened. 

 The hinge-line straight and moderately long. The umbo of the left valve 

 triangular, pointed, and moderately convex ; that of the right valve flattened and 

 almost obsolete. 



Interior. — Smooth, with obscure radiating ribs towards the margin. 



Exterior.- — The surface of the left valve is marked with many fine, close, 

 radiating ribs, between which new ones arise as they become separated in the 

 passage across the shell, the whole of which are crossed by subimbricating striae. 

 The posterior ear is marked with frequent radiating striae crossed by concentric 

 lines of growth, the ribs being further apart in the centre of the car than at the 

 upper or lower margin. The anterior ear is adorned in the same manner. The 

 right valve is very similarly ornamented, the secondary ribs, however, being often 

 wanting. The ears partake of the same character of ornament as those of the left 

 valve, but are smoother. 



I 'intensions. — PI. XII, fig. 6, Sowerby's type specimen, measures — 



Antero-posteriorly .... 37 mm. 



Dorso-ventrally .... 35 mm. 



Gibbosity of left valve . . . .3 mm. 



Localities. — England: the Carboniferous Limestone of Richmond, Yorkshire, 

 and Castleton, Derbyshire. Ireland: the Carboniferous Limestone of Little Island, 

 co. Cork ; Rathkeale, Kilgrogan, and Xantinan, co. Limerick ; Millicent, Clane, 

 co. Kildare; Clonaboy, co. West Meath ; St. Doulagh's, co. Dublin. 



