86 CARBONIFEROUS LAMBLLIBRANCHIATA. 



Several specimens from localities in East Lothian are in the collection of the 

 Geological Survey of Scotland, and among these are some with fewer and rather 

 coarser ribs. The left valve of A. gentilis, Sow., sp., may be mistaken for A. 

 Knoclronniensis, but the former shell has a smooth right valve. 



I consider P. bellis, M'Coy, to represent a young uncrushed example of the 

 species under discussion. The shape of the ears and general similarity of the 

 valve are very strik 



ery 



:mef. 



Aviculopecten gbntilis, J. de G. Sowerby, sp., 18-10. Plate XVII, figs. G — 10. 



Pecten gentilis, J. de G. Sowerby, 1840. In Prestwich's Geol. Coalbrookdale, 

 Trans. Geol. Soc, ser. 2, vol. v, pi. xxxix, fig. 19. 

 — scalaris, J. de G. Sowerby, 1840. Ibid., pi. xxxix, fig. 20. 



Aviculopecten pibrillosus, Hind, 1902. Trans. N. Staffs. Field Club, vol. xxxvi, 

 p. 80, pi. ii, figs. 4, 5. 



Specific Characters. — Shell small, the left valve convex, the right much less so, 

 obliquely ovate. The anterior margin short and convex ; the lower expanded and 

 rounded ; the posterior almost straight and oblique. The hinge-line medium size. 

 Umbones small, subcentral. Ears depressed, well defined from the shell both in 

 front and behind, the posterior prolonged and somewhat pointed. 



Interior. — Unknown. 



Exterior. — The right valve is smooth, with very fine microscopic concentric 

 lines, the ears with several radiating ribs, fewer and coarser on the anterior ear, 

 both crossed by fine concentric lines. The left valve is ornamented with numerous 

 fine raised ribs, between each pair of which soon arises a secondary rib. 

 Occasionally very fine concentric lines of growth are to be found. Both ears are 

 ornamented in a similar manner. The ribs on the anterior ear fewer and coarser 

 than on the right ear. 



Dimensions. — PL XVII, fig. 9, a specimen from Congleton Edge, Cheshire, 

 measures — 



Antero-posteriorly . . . .15 mm. 



Dorso-ventrally . . . .11 mm. 



Localities. — Pennystone Ironstone, Coalbrookdale ; below Third Grit, Congleton 

 Edge, Cheshire; below Third Grit, Eccup, Leeds. 



Observations. — The figure of J. de C. Sowerby's Pecten gentilis in Prestwich's 

 memoir above cited is \ovy well drawn, and shows the peculiar form of the left 

 valve very well. No mention is made of the rigid valve. A shell, said to be the 

 type, is in the collection obtained Prom the Late Sir Joseph Prestwich at the 



