CARBONIFEROUS FOSSILS OF IRELAND. 95 



PeCTEN INTERCOSTATUS. M'Coy. (PI. XVIIL fig. 4). 



Sp. Ch . — Shell oblique ; surface with about nine or ten strong, radiating ribs ; between these are from three 

 to nine smaller, the middle one of which is usually larger than the rest ; all the ribs have fine, compressed, 

 hooked spines at regular intervals, which, when broken, give them a tubercular aspect ; cars very large, square, 

 with radiating ridges, and strong spines on the dorsal margin. 



This beautiful little shell appears very closely allied to the P. interstitialis, Phil., but the number of small 

 ribs between every two large ones, instead of being regularly three, is seldom less than five, and as frequently 

 nine, on the one specimen ; the ears also differ materially. It is very seldom that any of the delicate spines are 

 preserved, the ribs more frequently presenting a roughened or tuberculated aspect. Length six and a half 

 lines, width seven and a half lines. 



Pecten interstitialis. Phil. 



Pecten interstitialis. Phil. Geol. York. 



Sp. Ch. — Obliquely ovate; ears small, acute; about eighteen sharp, radiating, spinose ribs, in the spaces 

 between which are three smaller ribs, or striee. 



This species has nearly equal, acute ears, which are striated both radiatingly and across ; the three elevated 

 striae between each pair of large, spinous ribs are very regular. Length seven lines, width six and a half 

 lines. 



Pecten irregularis. M'Coy. (PI. XV. fig. 8). 



Sp. Ch. — Longitudinally ovate, ornearly orbicular, convex; ears moderate, nearly equal, marked with 

 about five radiating ridges, crossed by fine striee, parallel with the outer margin ; body of the shell radiated with 

 about twenty-six flattened ridges, very irregular in thickness and length, intervening spaces smooth. 



This little species occurs in company with the P. bellis, M'Coy, which it much resembles ; it is distin- 

 guished, however, constantly, by the flatness and irregularity of the radiating ridges, wliich also gives them 

 the appearance of being more crowded, although really less numerous, than in that shell. Length two lines, 

 width two lines. 



Pecten JoNEsn. M'Coy. (PL XVI. fig. 10). 



Sp. Ch Obliquely obovate, convex; ears unequal, finely striated, parallel to the margin, anterior largest, 



connected with the body of the sliell by a flat space, posterior ear slightly pointed ; body of the shell with 

 about twenty-eight narrow, rounded, radiating ribs, three or four times their diameter apart, intervening spaces 

 smooth, slightly and irregularly wrinkled concentrically. 



This species is remarkable for the distinctness of its striation, the slender, radiating ridges being widely 

 separated, and each continuing distinctly up to the beak ; there are no radiating strite on the ears. Length 

 six lines, width seven lines. 



Pecten Knockonniensis. M'Coy. (PI. XVII. fig. 4). 



Sp. Ch. — Longitudinally ovate, convex; valves dissimilar, the one marked with close, fine, smooth, radiat- 

 ing striae, slightly flexuous, and nearly equal in size, the other radiated with about twelve large, rounded ribs, 

 each having a very fine, sharp, ridge on each side, each set of three ribs being separated from the next by a 

 narrow, flat space, all the radiating ridges on this valve are closely set with small, imbricating, scale-like lamina 

 of growth ; ears unequal, marked with radiating ridges crossed by fine lines of growth. 



This very beautiful species closely resembles the P. transversus of Devonshire, but is distinguished by its 

 smaller size, and the length considerably exceeding the width, the reverse of the proportions in the Devo- 



