OBLIQUIPECTEN LiEVIS. 115 



Observations. — Tins is a very curiously shaped shell, with a strong Pectiniform 

 character; but one cannot look at the left valve without the Ostrea-like form calling 

 for comment. The right valve is the more common. A single specimen of the 

 left valve from Settle is in the Woodwardian Museum, Cambridge, and I know 

 no other. 



Obliqtjipecten l.evis, sp. nov. Plate XIX, figs. 1, 2. 



Specific Characters. — Shell of moderate size, compressed, obliquely extended in 

 front, truncate behind, very inequivalve, the right valve being the more convex ; 

 very inequilateral, the posterior portion being almost obsolete. Anterior border 

 descending from the umbo, curved rapidly outwards so that the edge of the valve is 

 deeply concave in the region of the anterior ear, the valve below this becoming 

 very convex. The lower margin convex, the posterior margin more gently curved. 

 The hinge-line short, especially behind the umbo, which is flattened, pointed, and 

 curved forwards, placed at the junction of the posterior and middle thirds of the 

 hinge-line. The anterior ears large, especially that of the right valve, which is 

 expanded above the hinge-line and deeply notched for the byssus below. The 

 posterior ears very small, but definite. The right valve bent suddenly on itself 

 along a curved line which passes downwards and forwards from below the posterior 

 ear, the angle of flexion gradually becoming less as it approaches the lower border. 



Interior. — Unknown. 



Exterior. — The surface is almost smooth, but the microscope shows it to be 

 ornamented with fine concentric striae and lines of growth. The right anterior ear 

 has concentric lines, and the left ear shows fine radiating lines. 



Diiiw-nsioiis. — PI. XIX, fig. 2, a left valve from Settle, measures — 

 Antero-posteriorly . . . .37 mm. 



Dorso-ventrally . . . .45 mm. 



Localities. — England : the Carboniferous Limestone of Settle and Hill Bolton, 

 Yorkshire ; Castleton, Derbyshire ; and Narrowdale, Staffordshire. 



Observations. — This very peculiarly shaped species is not likely to be confounded 

 with any other. The right valve is recognised by the marked flexure of the valve 

 near its posterior border. The Woodwardian Museum, Cambridge, has a set of 

 seven specimens from Settle, six of which are right valves. The peculiarly 

 expanded anterior ear, with its deep slit for the byssus, is not met with in other 

 Pectiniforni shells. The species is not common, but I have found it myself in the 

 localities named above, which are all on the same horizon. 



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