54 CARBONIFEROUS LAMELLIBRANCHTATA. 



ribs. I have not noticed one rib dividing or coalescing with another. The 

 concentric lines of growth are rarely very distinct, but they are occasionally so 

 well marked as to interrupt the radiating ribs and cause a more or less widely 

 reticulate appearance. I am unable to agree with Mr. R. Etheridge, jun., that the 

 radiating ridges frequently bifurcate. I have never seen such a condition, and think 

 he must have been misled by the intercalated ribs, which on careful examination 

 are found to arise independently in the spaces between the primary ribs. The 

 shell varies considerably as to the number and closeness of the radiating ribs. The 

 ribs are strongest and widest apart on the posterior ears. 



A personal examination of the type specimen of Aviculopecten Mosensis, 

 de Koninck, leaves no doubt in my mind that the latter name is a synonym of 

 P. papyraceus. The matrix of the fossil is a black limestone, and therefore not the 

 Vise Limestone. It belongs to a horizon at Vise above the massif, and indicates 

 beds of the Pendleside series. 



I also think that the Avicula Samuelsii of Brown, described and figured in 

 ' Trans. Manch. Greol. Soc.,' vol. i, 1841, p. 225, pi. vii, fig. 65, is the young of 

 P. papyraceus. 



Pterinopeoten concavus, M'Coy, sp., 1884. Plate IX, figs. 6, 7. 



Pecten concavus, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 90, pi. xv, fig. 10. 

 Aviculopecten concavus, M'Coy, 1854. Brit. Pal. Foss., p. 484, pi. 3 e, fig. 2. 



Specific Characters. — Shell of medium size, transversely quadrato-orbicular, 

 only moderately convex. The anterior, inferior, and lower part of the posterior 

 margin convex, the upper part of the posterior border sinuous. The umbones 

 small, pointed, not raised. The hinge-line long and straight. The anterior ears 

 long, large, and well defined, especially in the right valve, the posterior ears not 

 well marked off from the body of the valve, long, their depth indicated by an 

 extension of the posterior border in a falciform manner. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with numerous close, fine, rounded, 

 radiating ribs, new ones becoming intercalated between them as they pass towards 

 the margin of the valve. The ears are ornamented in the same way as the rest of 

 the valve. The ribs are crossed by concentric lines of growth, which are here and 

 there more or less deeply marked, best seen at the posterior border and posterior 

 car, where the radiating stria) are interrupted by them. 



Dimensions. — PL IX, fig. G, the type of Aviculopecten concavus, M'Coy, 

 measures — 



Antoro-posteriorly .... ( .>imm. 



Dorso-vcnt rally .... 70 mm. 



