114 CARBONIFEROUS LAMELLIBRANCHTATA. 



Localities. — England: the Carboniferous Limestone of Castleton, Derbyshire; 

 Poolvash, Isle of Man ; Underset Limestone of Farcote Gill, Wildboar Fell, West- 

 moreland. Scotland : the Lower Limestone series of Thornton. Ireland : the 

 Carboniferous Limestone of Bruckless, Dunkineely, co. Donegal. 



Observations. — M'Coy founded his species on a mere fragment, probably the 

 impression of the exterior of a right valve, but not possessing sufficient details to 

 warrant the drawing of the anterior ear. The peculiar character of the numerous 

 fine radiating ribs is, however, well marked in the type-specimen. 



The large and almost smooth posterior ears, quite free in their greater part 

 from radiating ribs, is an important character, and prevents any confusion between 

 this shell and Pterinopecten concavus, which has a somewhat similar marking, but 

 differs totally in the characters of its ears. There seems to belittle or no difference 

 between the convexity and markings of both valves. 



I am able to figure both valves. The left valve (PL XV, fig. 21) is from the 

 cabinet of Mr. R. Law, who obtained the specimen from Castleton. The right 

 valve is a specimen from Derbyshire in the Wood Collection, York Museum 

 (PI. XV, fig. 23). I obtained a fragment, showing the hinge-plate, from the Under- 

 set Limestone, high up in the Yoredale Series of Lunedale. It shows the peculiar 

 ears and markings of M'Coy's shell, in addition to the characteristic hinge-plate of 

 Grenipecten. The hinge-plate is a little imperfect at the centre, and evidently 

 belongs to a right valve (PI. XV, fig. 22). 



G. semicircular is, M'Coy, closely resembles G. WincheUi from the Waverlev 

 Sandstone, Newark, Ohio, but has a rather longer hinge-plate, and is generally 

 more transverse. It seems to me that Hall was mistaken in stating that the 

 anterior ear is larger than the posterior ear. PI. ix, figs. 27, 28, of his monograph, 

 evidently represent left valves, as he states they show the posterior ear to be the 

 larger; but, as I have quoted above, he regards G. WincheUi as an aberrant 

 generic form. It is interesting, therefore, to see a shell with such similar characters 

 present in the Carboniferous Strata of England. 



Genus Obliquipecten, nov. 



Generic Character's. — Shell compressed, with the anterior end much developed; 

 (he posterior end almost obsolete. The left valve flattened, with a large anterior 

 ear ; posterior ear almost obsolete. The right valve with a large anterior ear, the 

 posterior part of the valve bent on itself obliquely downwards and forwards. 

 Hinge-line small. Umbones pointed, curved forwards, and flattened. 



Exterior. — The surface, almosl smooth, is ornamented by fine concentric lines 

 of growth. 



