PSEUDAMUSIUM REDESDALENSE. 109 



somewhat compressed, hence its flattened condition. An almost perfect bivalved 

 example is in the collection of the Geological Survey of Ireland (PL XVI, fig. 25). 



The name P. auriculatum has been adopted, as it occurs in M'Coy's work several 

 pages in advance of Pecten cingendus, and therefore has the priority. 



His species is easily distinguished from A. Sedgwichi, in which shell the 

 concentric ribs are angular and acute. It seems to me that the species is most 

 likely to be mistaken for small, incomplete specimens of Posidoniella vetusta, in 

 which there is no anterior ear, and the whole shell is more oblique. Aviculopecten ? 

 concentrico-costatus, de Koninck, is probably a young form of M'Coy's species, 

 which accounts for the number and closeness of the concentric ribs. 



The type of Lima laevigata, M'Coy (PI. XVI, fig. 2-t), is evidently only a full- 

 grown example of the left valve of P. auriculatum distorted by shearing. 



Pseudamusium Redespalense, sp. nov. Plate XX, figs. 1 — 6. 



Specific, Characters. — Shell below medium size, obliquely suborbicular, sub- 

 equivalve, the left valve the more convex. The margin one single curve, most 

 convex and produced in front; the hinge-line short and straight. The umbones 

 small, pointed, very slightly raised, and situated about the centre of the hinge-line, 

 and therefore posterior to the middle vertical diameter of the valves. The ears 

 small, the anterior in the right valve well defined, divided from the valve by a 

 deep, broad, scimitar-shaped groove for the byssus, that of the left valve triangular 

 and sharply depressed. The posterior ears small and triangular in both valves, 

 their posterior margin vertical. 



Interior. — The adductor muscle-scar is large, oval, and placed posterior to the 

 middle line above the centre of the valve from above downwards. The pallial line 

 is remote from the margin. The inner surface of the left valve below the pallial 

 line is marked by flat radiating ribs, the right valve being quite smooth. Mat 

 radiating colour-bands of considerable thickness often present. The hinge shows an 

 elongate groove for the ligament. 



Exterior. — The surface of the right valve is smooth, but the anterior ear has 

 imbricating concentric lines. The left valve has almost obsolete, flat, radiating 

 ribs, covered with tine, close, linear, radiating striae in its lower two-thirds. 

 Apparently smooth in the upper third. 



Dimensions. — PI. XX, fig. 3, a bivalved example, measures — 



Antero-posteriorly .... 25 mm. 



Dorso-ventrally . . . . 25 mm. 



From side to side . . . . 8 nun. 



