74 CARBONIFEROUS LAMELLIBRANCHIATA. 



Observations. — The type of Sowerby's Pecten plicatus is preserved in the 

 Sowerby Collection of the Natural History Musenm, South Kensington. It is a 

 left valve (PI. XII, fig. G), a little damaged at the umbo and posterior ear. It was 

 obtained from Queen's County, Ireland. I have studied the right valve from speci- 

 mens in the collection of Mr. Joseph Wright, of Belfast, and one of these is figured 

 (PI. XII, fig. 8). It lies on a slab only slightly separated from a left valve of the 

 same species, and they probably belonged to each other. There is no doubt Pecten 

 Mans, M'Coy, is identical with Sowerby's species. The diagnosis of the latter is as 

 follows : — " Longitudinally ovate, depressed ; ears small, unequal ; a very large 

 fold beneath the posterior ear forming a hiatus in the margin. Surface with very 

 numerous, rounded, radiating ridges, alternately larger and smaller, crossed by 

 regular, concentric, imbricating stria?. This shell is rendered very remarkable by 

 the large fold on the posterior side," etc. etc. The type of P. hians, M'Coy, is in 

 the Griffith Collection, Museum of Science and Art, Dublin. It is a very imperfect 

 example of the left valve, but shows the characteristic posterior fold, which is 

 almost all that remains of the real shell. I have therefore not re-figured it. I 

 regard this peculiarity as typical of A. plicatus, Sowerby, sp., and I have hitherto 

 not met with this character in any other Carboniferous species. P. micropterus, 

 M'Coy, is a name given to a young specimen of A. plicatus, and must be placed 

 amongst the synonyms of this species. 



Phillips doubtfully referred a shell to Pecten plicatus. I have been able to 

 compare this with the type, and certainly they do not belong to the same species. 

 Phillips's shell (PI. XIII, fig. 10) is much more convex, the ribs are much stronger, 

 the posterior ear is small and depressed. This shell shows doubtless the external 

 characters of P. semicostatus of Portlock, a species founded on an internal cast, to 

 which I now refer it. 



AvrcuLorECTEN Eskdalensis, sp. nov. Plate XII, figs. 7, 10, 11. 



Specific Characters. — Shell inequivalve, of medium size, obliquely quadrato- 

 ovate. The left valve moderately convex, the right valve flattened. The margin 

 rounded. The hinge-line straight, almost as long as the transverse diameter. The 

 anterior ear in the right valve well marked, separated from the rest of the valve 

 by a slit for the byssus ; the ear in the left valve depressed, rolled, and well 

 defined from the body of the valve. In both valves the posterior ears seem to be 

 merely a depressed portion of the valve, triangular, deep, with the upper border 

 prolonged backwards and the posterior margin falcate. The umbones obtuse, sub- 

 central, not raised. 



Interior. —Unknown. 



