100 CARBONIFEROUS LAMELLIBRANCHIATA. 



diameter much less than the dorso-ventral diameter, ovato-rectangular. The 

 anterior margin of the valve slightly convex, the lower margin much more so, the 

 posterior margin almost straight. The hinge-line straight. Ears large and 

 depressed, pointed, with each margin falcate ; the right anterior ear deeply grooved 

 for the byssus. The posterior ears very deep and long, the fold separating them 

 from the valve reaching the margin low down. Umbones small and pointed, 

 placed in front of the centre of the hinge-line. 



Interior. — Unknown. 



Exterior. — The surface is ornamented with several distant, obscure, broad, 

 radiating ribs, separated by shallow grooves. The whole surface seems to be 

 smooth. Occasionally there are concentric lines and rugae of growth. The ears 

 have much the same characters as the rest of the valve. 



Dimensions. — PI. XIV, fig. 14, a left valve, measures — 



Antero-posteriorly . . . .37 mm. 



Dorso-ventrally . . . .53 mm. 



Locality. — Scotland: the Carboniferous Limestone series of Chance Pit 21, 

 Kivmeil, near Boness (roof of Smithy Coal). 



Observations. — This very characteristic species is founded on a right and left 

 valve on one surface of a slab of shale, and a smaller left valve on the other surface. 

 It would seem that this specimen is referred to in the memoir of the Geological 

 Survey of Scotland, explanation of sheet 31, p. 70, as Aviculopecten (near A. plano- 

 costatus, M'Coy, sp.). It is accompanied by a marine fauna, but many of the species 

 mentioned in the list are not named with certainty. Of course this shell has no 

 affinity with A. planocostatus, M'Coy, sp., which has quite distinct characters; but 

 the original drawing is so hypothetical that it is not to be wondered that other 

 shells have been confused with it. This species is now referred to the genus 

 Amusium (see p. 123). 



The left valve of A. inequalis seems to have been much larger than the right 

 valve, and to have overlapped this on all sides except that of the hinge-line. I 

 have not noticed this character in any other Carboniferous Pectiniform shell ; 

 otherwise the shape of the left valve is very similar to that of A. Murchisoni. 



Aviculopecten deoenatus, Phillips, sp., 1 83G. Plate XVIII, figs. 10 — 14. 



Pecten deornatus, Phillips, 1836. Geol. Yorks., pt. ii, p. 213, pi. vi, fig. 26. 



M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 91. 

 Amusium ? deornatum, M'Coy, 1855. Brit. Pal. Foss., p. 478. 



Specific Characters. — Shell small, broadly ovate, moderately convex, equi valve, 

 almost equilateral. The lower margin almost semi-circularly curved. The hinge- 



