POSIDONOMYA RADTATA. 31 



Specific Gliaracters. — Shell of medium size, irregularly subquadrate, compressed, 

 very sliglitly oblique, very inequivalve. There is a small anterior ear, making the 

 anterior superior angle a right angle. The border then descends downwards and 

 slightly forwards. The lower border is bluntly rounded and extended. The 

 posterior margin straight, somewhat oblique. The posterior superior angle ol)tuse. 

 The hinge-line straight, the shortest transverse diameter of the valve. The 

 umbones are small, tumid, pointed, placed anteriorly. The body of the valve is 

 gently swollen, compressed posteriorly to form a narrow posterior dorsal slope. 



Interior. — Unkno-wm. 



Exterior. — The surface is covered by irregular, concentric wrinkles and flattened 

 folds, crossed by obscure radiating wrinkles or ribs, more marked towards the 

 median and lower portion of the valve. Periostracum moderately thick. 



Dimension. — PI. VI, fig. 4, measures — 



Antero-posteriorly . . . . 1 o mm. 



Dorso-ventrally . . . .12 mm. 



Localities. — England : the Pendleside series, river Ribble, Dinckley Hall, 

 Lancashire. Scotland : in the East Kilbride district in the shale above, and in 

 the Calderwood cement-stone Old Quarry, south of Arkleston Print Works, 

 Paisley; Jamestouburn and No. 9 Pit, Blair, Dairy; Thornliebank ; Burn, near 

 Little Brodlie Smithy, Ayrshire. Ireland : the Upper Limestone Shales of 

 Garristown and Loughshinny. 



Observations. — This species was described and figured by R. Etheridge, jun. 

 (op. supra cit.). The shell is very often found crushed, when it may be mistaken 

 for Posidoniella Isevls or P. minor. The possession of an anterior ear, however, at 

 once distinguishes Etheridge's species from either of these. 



It appears that this species was at first referred to Anomia {op. supra elf.'). Like 

 other members of the genus, it possesses a strong and well-marked periostracum. 



PosiDOXOMVA EADiATA, sp. uov. Plate VI, figs. — [K 



specific Characters. — Shell below medium size, obliquely subcircular, very 

 moderately convex, equivalve, somewhat inequilateral. The anterior end is com- 

 pressed and expanded into tlie form of a small triangular ear at the antero-superior 

 ano-le, which is almost a right angle. The border passes downwards with a regular 

 curvature, and passing without break into the convex lower margin. The posterior 

 border is almost straight and oblique. The postero-inferior angle marked, but 

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



