52 CARBONIFEROUS LAMELLIBRANCHIATA. 



Aviculopecten papyraceus, Morris, 1854. Cat. Brit. Poss., 2nd edit., p. 165. 

 M'Coy, 1855. Brit, Pal. Foss., p. 488. 

 Salter, 1864. Mem. G-eol. Surv., Country round 

 Oldham, pi. i, fig. 1. 

 — Baity, 1875. Char. Brit, Poss., pi. xxxix, fig. 1. 



Boemer, 1876. Lethaea Geogn., taf. 44, fig. 1. 

 B. Etheridge, jun., 1876. G-eol. Mag., dee. 2, vol. iii, 

 p. 152, pi. vi, fig. 7. 

 1877. Ibid., vol. iv, p. 243, pi. xii, 

 figs. 4, 5. 

 Mosensis, de Koninck, 1885. Ann. Mus. Boy. d'Hist. Nat. Belg., 

 torn, xi, p. 214, pi. xxxvi.fig. 20. 

 papyraceus, Wild, 1892. Trans. Manch. Geol. Soc., vol. xxi, 

 p. 395, pi. iii, fig. 12. 



Specific Characters. — Shell semi-oval, inequilateral, slightly oblique towards the 

 posterior side, the left valve very moderately convex, the right valve much less so. 

 The anterior border very slightly convex, the lower strongly curved, the posterior 

 convex below and concave above. The hinge-line straight and long, the longest 

 antero-posterior diameter of the valve. Umbones small, and only slightly tumid, 

 the right less swollen than the left, placed about two-fifths the length of the hinge- 

 line from the anterior end. The anterior ears more definite than the posterior, 

 that of the right valve being the more distinct and separated from the valve by a 

 deep groove, which is represented at the margin by a deep notch for the byssus. 

 The left ear convex, not incised, margin only slightly notched. The posterior cars 

 not marked off from the rest of the valve, and only indicated by the gradual 

 compression of the valve. The postero-superior angle extending slightly beyond 

 the rest of the margin, so that the border of the valve shows a slight concavity 

 just below it. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with many somewhat irregular, flattened, 

 radiating ribs, secondary ribs often arising between the original ones, which pass 

 without dividing to the border. At times these ribs are decussated by lines of 

 growth, which vary much in degree in individual shells. Ears have a similar 

 ornament to the rest of the valve, but the lines of growth are much more marked 

 in these positions. The number and closeness of the ribs also vary. The ribs are 

 separated by smooth, flattened spaces. 



Dimensions. — PI. VII, fig. 13, a left valve from the Lower Coal Measures of 

 Southowram, measures — 



Antero-posteriorly . . . .60 mm. 



Dorso-ventrally . . . .53 mm. 



Convexity of left valve . , . ,5 mm. 



