GASTEROPOD FAUNA IN THE MILLSTONE GRIT OF SCOTLAND. 339 



more widely separated over the middle portion of the valve, becoming very fine and 

 close on the compressed part of the valve, so as to appear obsolete to the naked eye. 

 These radiating ribs are crossed by concentric, irregularly distributed lines and rugae 

 of growth. 



Dimensions. — PL I. fig. 11. Specimen No. T2982 B measures: antero-posteriorly, 

 15 mm. ; dorso-ventrally, 14 mm. 



Localities. — Linlithgow, river Avon, E. side of the Kailway Viaduct, 35 to 40 

 feet above the Castlecary Limestone. 



Observations. — A number of specimens of this species have been obtained, but from 

 only one of the localities. The species agrees with the description given by Meek 

 (op. supra cit.), but is somewhat larger than his figured specimens. In the adult state 

 the posterior margin becomes sinuous above, a fact not indicated in the small American 

 specimen. The species has some affinity to P. carbonarius, Hind, but the ribs are 

 broader and flatter and more flexuous, and more interrupted by concentric lines of 

 growth. The distribution of P. carbonarius extends from fairly low down in the 

 Pendleside series to the middle of the Coal Measures. 



Pterinopecten papyraceus, Sow., sp. 



I refer two fragments to this well-known species, one from the Linlithgow and the 

 other from the Gair locality. Undoubted specimens, however, were obtained from the 

 Bilston Burn. I feel fairly satisfied with my diagnosis, even in the fragmentary state 

 of the specimens. It is at this horizon that I should expect the species to occur in 

 force. In the Midlands it occurs immediately above the upper beds of Carboniferous 

 Limestone or the beds denoted by the coral genera Cyathaxonia and Amplexi 

 zaphrentis. 



Aviculopecten carboniferus, Stevens, sp., 1858. (PL I. fig. 14.) 



Pecten carboniferus, Stevens, 1858, Amer. Journ. Sci. and Arts, vol. xxx. p 261. 



„ Broadheadii, Swallow, 1862, Trans. St Louis Acad. Set., vol. ii. p. 97. 



,, Hawni, Geinitz, 1866, Carb. und Dyas in Nebraska, p. 36, pi. ii. fig. 19, a, b. 

 Aviculopecten carboniferus, Meek and Hayden, Fin. Rep. U.S. Geol. Surv. Nebraska, p. 193, pi. iv. 



fig. 8 ; pi. ix. fig. 4, a, b. 



Specific Characters. — Body of the shell triangularly ovate, convex, greatest length 

 and breadth equal. The hinge line is moderately elongate, the umbones pointed, raised, 

 and central. The inferior border is broadly rounded, the margin interrupted by the 

 projection of the ribs as pointed processes. The anterior ear is large, compressed, 

 somewhat rolled, its upper border projecting and its anterior edge prolonged into a 

 point ; the posterior ear larger than the anterior, pointed, its margin falcate. The 

 ears are separated from the body of the valve by a deep concave sulcus. 



Exterior. — The surface is ornamented with few (15) distant, regular, raised, rounded 

 ribs, occasionally nodulose when they are crossed by transverse lines of growth. These 

 ribs project beyond the lower margin in the form of spines. 



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