190 BRITISH CARBONIFEROUS BRACHIOPODA. 



Loc. Carboniferous slate of Rahoran, Eivemile Town, Ireland. 



Obs. Prof. M'Coy states that this species seems closely allied to that which he has 

 figured under the name of Leptcena serrata, but is distinguished by its angular plaits and 

 rounded extremities, the radiating ridges being striated transversely. I have examined 

 the original example, and must say that it appeared to me to be nothing more than a small 

 specimen or young shell of C. Hardrensis. Prof. M'Coy has exaggerated the inward 

 curve of the spines, and the enlarged illustration of the striae is not correct, being exactly 

 similar in the specimen to what we find in C. Hardrensis. 



Chonetes polita, M'Coy. PL XLVII, figs. 8—11. 



Leptcena (Chonetes) polita, M'Coy. British Palseozoic Fossils, p. 456, pi. iii u, 



fig. 30, 1855. 



Spec. Char. Shell transversely semicircular, concavo-convex j hinge-line slightly 

 longer than the width of the shell, with a narrow, sub-parallel area in either valve, the 

 ventral one, which is the widest, being divided in the middle by a small fissure, arched 

 over with a pseudo-deltidium, both valves being articulated by the means of teeth and 

 sockets ; ventral valve gibbous, much vaulted in the middle and at the beak, which last is 

 small, and does not overlie the cardinal edge ; dorsal valve concave, following the curves of 

 the opposite one. Surface of both valves smooth, and marked only by fine, concentric lines 

 of growth, a few scattered spines rising from the surface of the larger valve, and two or 

 three longer ones project from the cardinal edge on either side of the beak. In the 

 interior of the ventral valve the muscular impressions are very feebly marked, and are 

 divided by a small mesial ridge or septum, while pustule-markings rise from the whole 

 remaining surface. In the interior of the dorsal valve, under and a little lower down than 

 the cardinal process, there exists four small impressions left by the adductor or occlusor 

 muscle, while two prominent ridges divide the central pair, and are prolonged to about 

 two thirds of the length of the valve, the remaining portion of the valve being covered with 

 elongated pustular markings. Dimensions very variable ; two specimens have measured — 



Length 2|, width 3 lines. 

 5, 2 ,,2 ,, 



Obs. This remarkable little shell is at once distinguished from all its congeners by 

 the smoothness of its valves, as well as by the two peculiarly prominent ridges in the 

 interior of the dorsal valve, and which are likewise present in one or more Silurian species. 

 Prof. M'Coy remarks that this form has much the shape of C. volva, but is not so 

 wide, is more gibbous, and is the only Carboniferous species he knows that has a smooth 

 surface. 



In England it is stated by Prof. M'Coy to be rare in the dark Carboniferous limestone 

 of Lowick, Northumberland, that it occurs at Mount Rath, in Ireland, and we are indebted 

 to the great zeal of Mr. Young for his discovery in Scotland, and where it occurs in vast 



