130 CARBONIFEROUS LAMELLTBRANCHIATA. 



Dimensions. — PI. XXV, fig. 10, M'Coy's type, measures — 



Antero-posteriorly . . . .11 mm. 



Dorso-ventrally . . . .17 mm. 



Localities. — England: the Carboniferous Limestone of Hill Bolton, Yorkshire. 

 Scotland : the Upper Limestone Series of Orchard. Ireland : the Carboniferous 

 Limestone of Black Lion, co. Leitrim. 



Observations. — The type of this species is a left valve, not very well preserved, 

 contained in the Griffith Collection, Science and Art Museum, Dublin, PI. XXV, 

 fig. 10. I have fortunately been able to study other examples, namely two very 

 large valves in the collection of Mr. J. Neilson (one figured, PI. XXV, fig. 9), and 

 a left valve from Hill Bolton, in my collection. The latter, a left valve, shows the 

 characteristic markings very well. I am not sure whether this species should be 

 referred to Aviculopecten on account of the short posterior ear. 



Aviculopecten constans, de KonincJc, 1885. Text-fig. 1. 



Aviculopecten constans, de Koninch, 1885. Ann. Mus. Roy. d'Hist. Nat. Belg., 

 torn, xi, p. 226, pi. xxxviii, figs. 13, 14. 



Specific Characters. — Shell of medium size, suborbicular, moderately convex. 

 The hinge-line shorter than the transverse diameter, the inferior margin broadly 



Text-fig. 1. — Aviculopecten constans, de Kon. 



subcircular. The umbo acute, central, ears marked off from the valve by well- 

 marked curved lines with the concavity upwards, leaving the umbonal portion 

 triangular. The anterior ear the smaller, triangular, depressed, its anterior 

 border concavo-convex. The posterior ear the larger, with its upper border 

 produced, and its posterior border falciform. 



Interior. — Unknown. 



Exterior. — The surface of the valve is adorned with numerous fine, close, 

 radiating, raised lines, coarser near each margin, and with secondary lines arising 



