SEDGWICKIA ATTENUATA. 285 



ambones and upper part of the centre of the shell eroded, so that the lower 

 layers of the shell are exposed ; but it is doubtful whether any definite opinion as 

 to the habitat of this species can be based on the fact, Edmondia, sp., and Pecten, 

 sp., occurring at the same locality. I think that there is no doubt, however, 

 that the erosion of the valves is in this case due to the usual cause, that is the 

 presence of C0 2 in the water, and that possibly this is an indication of a strong 

 admixture of fresh with salt water, but a careful research into the fauna of the 

 bed is necessary to settle the question. 



Sedgwickia attbnuata, M'Coy, 1844. Plate XXVII, figs. 9, 11—14. 



Sedgwickia attenuata, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 62, pi. xi, 



fig. 39. 

 Lyonsia attenuata, cTOrbigny, 1850. Prodrome de Pal^ontol., p. 328. 

 Sedgwickia attenuata, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 224. 



— — ■ Bigsby, 1878. Thesaurus Devonico-Carboniferus, p. 311. 

 — Etheridge, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 290. 



— — Bariies and Holroyd, 1897. Trans. Manch. Greol. Soc, 



vol. xxv, p. 187, fig. 14, 3rd pi. 



Specific Characters. — Shell of less than medium size, transversely ovate, 

 moderately convex, inequilateral. The anterior end is short, convex, deep from 

 above downwards, and has a well-rounded border, somewhat elliptically curved. 

 The inferior margin is almost straight except at the extremities. The posterior 

 border is obliquely truncate from above downwards, almost straight, and narrowed, 

 the postero-inferior angle being bluntly rounded, the postero-superior being a well- 

 marked obtuse angle. The hinge-line is curved in front; produced, depressed, 

 and straight posteriorly. The umbones are tumid, not marked off from the shell 

 by folds, elevated, and situated in the anterior third of the valve. The valves are 

 regularly convex, but there is a well-marked ridge which extends from the umbo 

 to the postero-inferior angle, above which the shell is compressed and flattened. 



Interior. — The anterior adductor muscle-scar is shallow, elongate, situated 

 just within the antero-superior angle. The posterior is rounded, shallow, and 

 situated near the postero-inferior angle in the hollow of the dorsal slope. The 

 pallial line is entire and remote from the margin. The hinge is edentulous. The 

 interior exhibited obsolete concentric folds in the anterior part of the valve, and 

 very faint radiating strise over the middle and posterior portions. 



Exterior. — The surface seems to be ornamented with fine concentric lines of 

 growth, strong anteriorly but becoming obsolete posteriorly. 



37 



