34 CARBONIFEROUS LAMELLIBRAXCHIATA. 



are crushed. M'Coy states (oj). supra cit.) that " specimens frequently occur 

 nearly three inches in their longest diameter." 



The narrow obliquely elongate shape of the shell and the irregular wrinkles on 

 the surface at once distinguish the species from P. Becheri. It is interesting to 

 note that the two species are found in the same series of rocks in both England and 

 Ireland. 



When young it is not improbable that P. memhranacea may be confounded with 

 PosidonicUa Isevis, but the subcentral beaks and possession of an anterior ear 

 and greater obliquity can be relied upon as characteristic features in the 

 former. 



I can find no record of this species having been obtained pre\dously in 

 England. I, some years ago, obtained many specimens in much the same con- 

 dition as those from co, Dublin, in the bank of the river Wharf, south of the 

 stepping-stones at Linton, Yorkshire. Fragments of goniatites and Posidonomya 

 Uecheri were obtained with it, and more recently I have seen many specimens from 

 ihe same horizon at Pendle Hill, Dinckley Hall, and Holden. 



Mr. R. Etheridge, sen., indicates that P. membranacea occurs in the Lower 

 Limestone shales. Carboniferous Limestone, Upper Limestone shales (Yoredales), 

 and Millstone Grit series, but unfortunately he neither gives his authorities nor 

 quotes localities. I doubt the occurrence of the shell except in the Pendleside 

 series (the Upper Limestone shales of the Irish survey). 



Posidonomya lamellosa, de Koiiind; 1851. Plate VI, figs. 16 — 18. 



Posidonomya lamellosa, de Koninck, 1851. Descr. Auim. Foss. Belg , Supplenieut, 



p. 683, pi. Ivii, fig. 5. 

 — OBLiQUA, (le Koninck, 1885. Ann. Mus. Eoy. Hist. Nat. Belg., 



torn, xi, p. 182, pi. xxxi, figs. 21, 22. 



Hpecific Characters. — Shell below medium size, equivalve, somewhat inequilateral, 

 gibbose, obliquely ovate. The anterior border is almost straight, descending down- 

 wards and forwards ; the inferior border is broad and convexly curved ; the 

 posterior border is almost straight and oblique. The hinge-line is short and 

 straight, the antero-superior and postero-superior angles being well marked 

 and rather larger than right angles. The umbones are obtuse, pointed, incmwed, 

 and placed in the anterior third of the hinge-line. The valve is regularly but 

 obliquely swollen, with the antero-superior and postero-superior angles compressed 

 into small ears, the posterior being much the larger. 



Interior. — Unknown. 



I 



