EDMONDIA RUDIS. 303 



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

 remote from the margin in the hollow of the umbonal swelling. The posterior, even 

 more obscure, is situated in the hollow of the dorsal slope. There is an accessory 

 posterior muscle-scar placed at the posterior extremity of the narrow elongate 

 groove, parallel to the edge of the valve. The pallial line is almost obsolete, but 

 entire. The hinge is shown by casts to be edentulous. There is an elongate 

 flattened ossicle which is directed outwards and downwards into the umbonal 

 cavity. The internal surface shows obscure concentric grooves and rounded 

 ridges, but is on the whole smooth. 



Exterior. — The surface is ornamented with well-marked, unequal concentric, 

 rugose folds and grooves, which are, however, less mai'ked iu front and behind, 

 where the shell has a tendency to become smooth. 



Dimensions. — Fig. 8, Plate XXVIII, measures — 



Antero-posteriorly . . . .33 mm. 



Dorso-ventrally . . . .28 mm. 



From side to side . . . .19 mm. 



Localities. — England : one of the Limestones of Lowick, the Coombs Lime- 

 stone, near Redesdale, and Lewisburn, Northumberland ; the Carboniferous 

 Limestone of Thorpe Cloud and Castleton, Derbyshire ; the Cayton Gill beds, near 

 Harrogate, Millstone-grit series ; the Pennystone Ironstone, Coalbrookdale ; the 

 Upper Carboniferous Limestone of Poolvash, Isle of Man. Scotland : Lower 

 Limestone series of Newfield, High Blantyre ; Langside, Beith ; Craigenglen; 

 and Hind Og Glen, Dairy; Archerbeckburn, Canoubie, Roxburgh. 



Observations. — Since the type specimen of Corbula ? senilis, Phillips, has 

 disappeared, and the figure is poor and the description meagre, I think there may 

 be some little doubt of the species being identical with that described later by 

 M'Coy as Edmondia rudis. Under the circumstances, however, I am compelled to 

 adopt the later name, and to place Phillips's shell as a doubtful synonym, since 

 this species has never been redescribed or apparently adopted, except in mere 

 catalogues, probably on account of the loss of the type. 



This species is characterised by its rugose appearance and quadrate gibbose 

 form even in casts. In the West of Scotland, in the nodules of the shales of the 

 Lower Limestone series, it is perhaps the most common species of the genus ; but 

 it also is found in the upper beds of the Carboniferous Limestone of Derbyshire 

 and the Isle of Man, and as a dwarfed form in the Pennystone Ironstone of the 

 Coal-measures of Coalbrookdale. De Koninck seems always to have misunder- 

 stood the characters of Phillips's E. unioniformis, and I am of opinion that the 

 shells figured by him in his latter work as specimens of that species are small 

 examples of E. rudis, and I have no hesitation whatever in placing- E. rugata of 

 the same author as a synonym of M'Coy 's species. Speaking of his E. rugata, 



