POSIDOXOMYA MEMBRANACEA. 33 



PosiDONOMYA MEMBEANACEA, M^Coij, 1844. Plate V, figs. 18 — 23. 



PosiDONOMTA MEMBRANACEA, M'Co]], 1844. Sjuops. Cavb. Foss. Ireland, p. 78, 



pi. xiii, fig. 14. 



— — d'Orhigmj, 1851. Prod. Pak'ont., vol. i, p. 138. 

 — Morris, 1854. Cat. Brit. Foss., 2iid edit., p. 181. 



— — Baihj, 1875. Figs. Char. Brit. Foss., p. 114, 



pi. xxxix, fig. 5. 



— — BUjsby, 1878. Thesaurus Devouico-Carboniferus, 



p. 293. 



— — Etheridge, 1888. Brit. Foss., pt. 1, Palaeozoic, 



p. 276. 



Specific Characters. — Shell compressed, obliquely ovate, narrow transversely, 

 deep from above downwards. The anterior ear is small and rectangular. The 

 antero-inferior border is convex and produced, curving bluntly below to join the 

 elongate, oblique, almost straight posterior margin, both margins being subparallel. 

 The hinge-line is short, straight, the postero-superior angle very obtuse. The 

 umbones are small, slightly convex, not raised, subcentral, l)ut inclining to the 

 anterior side. The shell was gently arched from before backwards and above 

 downwards. The posterior ear is triangular, compressed and small. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with concentric wrinkles and folds of 

 growth, crossed by fine, somewhat obscure, radiating lines which pass from the 

 umbones to the lower border ; the lines are more apparent on the posterior ears. 

 Shell thin, periostracum Avell marked. 



Bimenmyns. — PL V, fig. 22, from Garristown, co. Dublin, measures — 

 From anterior superior to posterior inferior angle . 37 mm. 

 Length of hinge-line . . . .15 mm. 



Localifies. — England : Yorkshire, the Pendleside series or shales with Lime- 

 stone, river Wharf, below Linton Church; Lancashire, Clough above Little 

 Mearly Hall, Pendle Hill, and river Kibble, south-west of Dinckley Hall near 

 Clitheroe ; Mixon Hey Brook, near Leek, Staifordshire. Ireland : the Upper Lime- 

 stone shales of Skerries ; Garristown ; Newtown ; Courtlough, co. Dublin ; Bala, 

 CO. Mayo. 



Ohservations. — This species was figured and described in 1844 by M'Coy. Tlie 

 type, PL V, fig. 18, is preserved in the Griffith Collection, ^Museum of Science and 

 Art, Dublin. It was obtained from Skerries, co. Dublin, and is much compressed. 

 A number of specimens are in the museum of the Geological Survey of Ireland, 

 from the Upper Limestone shales of co. Dublin, but unfortunately all the specimens 



5 



