GO CARBONIFEROUS LAMELLIBRANCHIATA. 



likely to have been a rather ornamented form of P. granosus. De Koninck con- 

 trasts his species with A. Ruthveni, M'Coy, sp., with which it has no affinity, the 

 latter shell belonging to another type of the genus, and Aviculopecten nodulosus, 

 de Koninck, which is P. granosus, Sow., sp. A specimen from the Lower Lime- 

 stone Shales of Clonakilty, co. Cork (PI. XI, fig. 14), was erroneously identified by 

 Baily as Aviculopecten papyraceus, and was so labelled in the collection of the 

 Geological Survey of Ireland. PI. XI, fig. 13, represents a fine specimen of a right 

 valve in the AVoodwardian Museum, Cambridge. 



Pterinopecten bigidus, M'Coy, sp., 1844. Plate VIII, figs. 1 — 3. 



Orthis umbraculum, Portlock, 1843. Rep. Geol. Londonderry, p. 456, pi. xxxvii, 



fig. 5. 

 Meleagrina rigida, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 80, pi. xiii, 



fig. 16. 

 Cf. Malleus orbicularis, M'Coy, 1844. Ibid., p. 87, pi. xix, fig. 2. 



Specific Characters. — Shell of medium size, obliquely suborbicular, the left valve 

 moderately convex. The anterior end small above but expanding below, with a 

 very convex, thickened border. The inferior border rounded, the posterior border 

 convex below, sinuous above, and thin. The hinge-line straight and prolonged 

 backwards. The umbones moderately convex and pointed, that of the left valve 

 slightly raised above the hinge-line and placed far forwards. The anterior ear in 

 the left valve short, badly defined, its antero-superior angle pointed. That of the 

 right valve unknown. The posterior ear not marked off from the valve, but the 

 valve compressed and expanded into the prolonged hinge-line, and the posterior 

 border concave just below the postero-superior angle. 



Interior. — The adductor muscle-scar is shallow, large, and in the same position 

 as in Meleagrina. The hinge-plate is broad and long, extending from the antero- 

 superior angle for a little more than two-thirds the length of the hinge-line. It is 

 marked by transverse ridges and grooves, three or four in number, which in the 

 region of the umbo are bent upwards to form a very wide angle. This hinge-plate 

 is placed obliquely, the lower edge projecting considerably more inwards than the 

 upper edge. Immediately below the hinge-plate, in front, is a smooth, shallow 

 furrow, which separates the thickened anterior edge from the plate and 

 corresponds with the byssal opening in the right valve. 



Exterior. — The surface is ornamented by numerous slightly raised, narrow, 

 rough, rounded, radiating, distant ribs, which pass from the umbo to the margin. 

 Between these primary ribs other finer ribs arise at intervals, and there may be 

 from one to three of these between the original ribs, commencing at different levels 



