AVICULOPECTEN JONESII. 129 



versely rounded, the posterior oblique and almost straight. The hinge-line is 

 straight, and equals the antero-posterior diameter of the shell in extent. The 

 umbones are small, pointed, not raised, placed slightly in front of the middle line. 

 The anterior ear of the right valve is well marked off from the rest of the valve by 

 the byssal slit, that of the left valve not so deeply notched. The posterior ears are 

 not marked off from the rest of the valve, but are represented by a compressed and 

 expanded postero-superior angle. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with about eighteen to twenty-four broad 

 raised ribs, separated by flattened spaces. The anterior ribs curve outwards near 

 the lower margin ; the median ribs are almost straight and do not bifurcate, and 

 ribs seem to be absent over the postero-superior portion of the right valve. The 

 anterior ears are crossed by a few well-marked radiating ribs. 



Dimensions. — PL XXV, fig. 14, a right valve, measures — 



Antero-posteriorly . . . .13 mm. 



Dorso-ventrally . . . .11 mm. 



Localities. — Marine Bands below the Gin mine Coal, Nettlebank, Smallthorne ; 

 sixty-nine feet below the roof of the 4-feet coal, Cheadle, N. Staffordshire 

 Coalfield ; the Pendleside Series, Bosley Minn, Cheshire. 



Observations. — This species is distinguished from P. papyraceus by its quadrate 

 shape, the possession of fewer broader ribs, and the smooth ribless character of the 

 postero-superior part of the valve. 



Aviculopecten Jonesii, M'Coij, sp., 1844. Plate XXV, figs. 9 — 11. 



Pecten Jonesii, M'Goy, 1844. Synops. Carb. Foss. Ireland, p. 95, pi. xvi, fig. 10. 



Specific Characters. — Shell below medium size, obovate, convex. The anterior 

 margin is curved, the lower border almost circular, the posterior nearly straight. 

 The hinge-line is straight and of moderate length. The ears are unequal, the 

 anterior the larger and more depressed. The umbo is acute, central, not raised. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with many fine radiating, linear, wavy 

 lines, which pass from the umbo to the lower margin ; occasionally other lines arise 

 between the primary ones about the centre of the valve. These radiating lines are 

 crossed by distinct concentric lines and striae of growth, and towards the lower 

 margin the intervals between the lines are crossed by concentric, close, wrinkled 

 lines. The concentric striae are well marked on the anterior ear of both valves, 

 and there are no radiating striae on the posterior ears. 



