24 CARBONIFEROUS LAMELLIBRAXCHIATA. 



first concave, descends downwards and a little backwards for a considerable distance, 

 when it becomes broadly curved, and passes round to meet the posterior margin. 

 The posterior margin is obliquely truncate, slightly convex, the postero-superior 

 angle a right angle. The hinge-line is long and straight. The umbones are small, 

 very slightly raised, curved forwards, terminal. The body of the valve is convex 

 and adpressed in front, flattened and expanded posteriorly. The posterior wing is 

 large, triangular, separated from the valve by a broadly concave oblique sulcus. 

 Hinge-plate with linear grooves, edentulous. 



Interior. — Umbones of casts not quite anterior. Posterior adductor shallow 

 and obscure, placed beloAv the hinge-line, in the hollow of the dorsal slope, remote 

 from the posterior end. 



E.nipr'wr. — The surface is covered with coarse, rugged, irregular, flexuous, 

 slightly interrupted, radiating ridges, which are a trifle more regular on the 

 posterior wing. These ridges are crossed by very obscure occasional concentric 

 lines of growth. Shell thin. 



Dimensions. — PI. IV, fig. 9, M'Coy's type specimen, in the Woodwardian 

 Museum, Cambridge, measures — 



Antero-posteriorly . . . .28 mm. 



Dorso-ventrally . . . .28 mm. 



Thickness of valve . . . .5 mm. 



A fine specimen, PL IV, fig. 10, from Eskerhouse, measures — 



Antero-posteriorly . . . .88 mm. 



Dorso-ventrally . . . , . (30 mm. 



From side to side . . . .27 mm. 



Loailities. — England : the Carboniferous Limestone of Hill Bolton, Hollin Gill, 

 Hawes, Eskerhouse, Widdale Beck, Apperset, Yorkshire ; Lowick and the Redes- 

 dale Limestone, Northumberland ; Black and White Limestone of Derbyshire, Park 

 Hill. Pendleside Series, "Black Limestone, River Wharf, Burnsall ; Dinckley Hall, 

 River Ribble ; Raven sclough, Thornley Hall, Hold en (Bolland), Lancashire ; Sulber 

 Lathe, Flasby Fell, Yorkshire ; Ford Village in River Hamps, Staffordshire ; 300 

 feet below third grit, Congleton Edge, Cheshire. Scotland: Lesmahagow; the 

 Upper Limestone series of Linnspout, Newcastle Glen and Corrieburn, Horwood ; 

 Lower Limestone series. Burn Anne, Cockmuir Bridge, Raven Crag, Kirkcaldy ; 

 High Blantyre, Teasses, Largo; Woolford Pit, Cobinshaw; Bilston Burn, Dryden. 

 First Limestone, Shore at Abden ; Esperston Quarry, South, near Borthwick; No. 

 IG Mine, Addiewell, West Calder; Lennoxburn, Old Quarry, Haddington; Quarry 

 Hebershaw Farm, Penicuick. 



Observations.— V\. IV, fig. 9, is M'Coy's type, from Lowick. It is the cast of a 

 left valve, which accounts for the absence of radiating ribs in the anterior part of 

 the valve. This specimen is not perfect posteriorly, consequently the contour of 



