PTERIXOPECTEN RADIATTJS. 55 



Localities. — England : the Carboniferous Limestone of Lowick, Northumber- 

 land. Ireland: Arenaceous Carboniferous Limestone of Killogunra, Killala. 



Observations.— This species has been described on two occasions by M'Coy. 

 The type used for the second description is from Lowick, and is in the collection 

 of the Woodwardian Museum, Cambridge. The specimen is a left valve, re-figured 

 in PI. IX, fig. 0, and I regard it as much crushed and flattened. In the same 

 collection and from the same locality are two other specimens, one being a right 

 valve (PI. IX, fig. 7), which is moderately convex, and as this valve is always less 

 gibbose than the left valve in all known species of the genus, it is reasonable to 

 suppose that the apparent flatness of the left valve is merely accidental. M'Coy 

 says that "this large species has the left valve counter outwardly in most speci- 

 mens, ... in which it differs from all other Palaeozoic species. The opposite 

 valve is slightly more convex," etc., etc. The ears have fine radiating ribs, being 

 marked exactly in the same way as the body of the valve. 



This shell might be mistaken for Aviculopecten semicircular!*, M'Coy, sp., if 

 I lie ears were not exposed ; in the latter species the posterior ears have no 

 radiating ribs, are better marked, and are almost smooth and much depressed. 



Pterinopeoten iudiatus, Phillips, sp., 183(>. Plate IX, figs. 12 — 16. 



Avicula kadiata, Phillips, 1830. G-eol. Yorks., pt. ii, p. 211, pi. vi, fig. 8. 



— Boscjuetiana, de Koninclc, 1851. Descr. Auim. Foss. Terr. Carb. Belg., 



Suppl., p. 082, pi. lvii, fig. 3. 

 Aviculopecten Bosquetianus, cle Koninclc, 1885. Ann. Mus. Roy. d'Hist. Nat. 



Belg., torn, xi, p. 215, pi. xxxv, figs. 29, 30. 



Specific Characters. — Shell below medium size, almost semicircular, very 

 slightly and transversely oblique, inequilateral, inequivalve, the right valve being 

 almost flat and the left somewhat convex. The anterior and inferior borders 

 convex, the posterior convex below, sinuous above. The hinge-line straight and 

 long. The umbones small, that of the left valve the more convex, pointed, and 

 placed a little posterior to the junction of the anterior and middle thirds of the 

 hinge-line. The anterior ears well defined, that of the left side marked off from 

 the rest of the valve by a sudden more or less deep oblique sulcus, which in some 

 specimens is almost obsolete. The same sulcus more pronounced in the right 

 valve. Posteriorly the ears not marked off in any way from the rest of the valve, 

 but formed by a gradual compression of the valve in this position, and their limit 

 marked at the posterior margin by a projection of the posterior superior angle and 

 the portion of the valve immediately beneath it. 



Interior. Unknown. 



Exterior.— The surface is ornamented by simple, distinct ribs of variable 



