EDMONDIA SULCATA. 319 



situated just within the antero-superior angle of the valve, and surmounted by 

 an excavated, elongate, pear-shaped accessory scar, which is deejDer and narrower 

 above, and is separated from the umbonal cavity by the process of shell (ossicle) 

 Avhich projects from the lower part of the hinge-plate, and from the edge of the 

 shell by the thickened hinge-plate. The posterior adductor scar is large, shallow, 

 and punctate, placed near the postero-superior angle in the hollow of the dorsal 

 slope. 



The hinge is simple and erect; but projecting from the back of the hinge-plate 

 into the hollow of the umbo is a large, curved, thin, expanded process, which 

 looks somewhat like a bivalve shell with umbones in front and a long, pointed 

 process posteriorly, the ossicle. The interior of the shell was deeply marked by 

 regular concentric grooves and ribs, the latter often bifurcating in front into two 

 thin, narrow ridges, with a tendency to more or less irregularity. There are faint 

 indications of radiating striaa over the body of the shell. Pallial sinus entire, 

 deeply marked, remote from the margin. 



Exterior. — The surface is ornamented with regular, broad, deep, concentric 

 ribs and sulci. The former are narrow and double at first, but unite sooner or 

 later, and towards the posterior end of the shell the ribs become thicker and 

 further apart, all, however, passing round, to terminate in the upper edge of the 

 valve. The periostracum is comparatively thick, and covered with fine, close, 

 regular, radiating rows of small tubercles, which pass indiscriminately over both 

 sulci and folds. Shell thin. 



Dimensions. — Fig. 6, Plate XXXIV, measures — 



Antero-posteriorly . . . .52 mm. 



Dorso-ventrally . . . .26 mm. 



Laterally . . . . .14 mm. 



Localities. — England : the Middle Limestone of West Witton, Wensleydale, 

 and from the neighbourhood of Richmond, Yorkshire ; one of the Limestones 

 of Lowick and the Redesdale Ironstone, the Lewisburn, near Plashetts, North- 

 umberland ; the Carboniferous Limestone of Kendal; the Upper Grey and 

 Middle White Limestones of Llangollen, North Wales ; Ballasalla quarry, Isle 

 of Man ; marine bed below the Millstone-grit of Congleton Edge, Cheshire ; the 

 Gannister beds, Snosterley, Durham. Scotland : the Lower Limestone series of 

 Beith ; Bathgate and Carluke; Brinston Colliery, Penicuik; Pot-metal, near 

 Kirkcaldy ; Lawston Linns, Liddlewater ; Muirburn, Newcastleton, Harelaw Hill 

 quarry, Roxburgh. Ireland : the Carboniferous Limestone of Rochfort Lodge, 

 Bundoran ; Kildare ; Grange Blundel and Arghamont, Armagh ; Derryloi-an and 

 Caledon, Tyrone. 



Observations. — In spite of the fact that Professor King pointed out that two 

 perfectly distinct shells were generally referred to the S. ? sulcata, Phillips and 



