SCHIZODUS OBOVATUS. 1 t3 



externally by a .slight curved ridge which starts from the umbo, and curving out- 

 ward, at first gradually approaches the margin, coalescing with it near the postero- 

 superior angle. 



The anterior part of the lower margin is much incurved, but gradually, being 

 twisted outward on itself, becomes flattened and depressed in its posterior half. 



Inferior. — The muscle-scars and pallial line have not been observed. The hinge 

 is multidenticulate, and the hinge-plate is much thickened. Anteriorly there are 

 several (seven) large oblique simple teeth, becoming larger as they approach the 

 front, with the exception of that one which is placed most anteriorly. These pass 

 just behind the umbo into a number of vertical, much smaller, closely-placed, 

 comb-like, simple teeth, which extend for some distance behind the umbo, and then 

 gradually become larger and oblique in position, each tooth slanting downward 

 and forward, and becoming more widely separated from its neighbour, the row of 

 teeth extending to within a small distance of the postero-superior angle. 



Exterior. — The surface is ornamented with fine close lines of growth, which 

 follow accurately the contour of the shell, being oblique to its long axis, and are 

 more marked in the region of the umbo, and on the dorsal slope, where they may 

 become subimbricate. 



Dimensions. — The specimen figured measures — 



Antero-posteriorly . . . .57 mm. 



Dorso-ventrally . . . .27 mm. 



Convexity of valve .... 12 mm. 



Locality. — England, in shales above the main mass of limestone in the beck, 

 south of Hammerton Hall, Slaidburn (Yorkshire). 



Observations. — Ctenodonta (Palseoneilo) lirata (Phill.), from the Devonian of 

 Baggy, has much the same kind of surface-marking as P. carbonifera, but differs 

 entirely in shape ; indeed, this species is quite distinct from any of the shells 

 belonging to the same genus, either from European or American Devonian 

 localities. I am unable to say anything about the fauna associated with P. 

 carbonifera at present, but beds of shale on presumably the same horizon at 

 Whitewell, a few miles farther south, contain the following fossils: Ctenodonta 

 Isevirostris, Nuculana attenuata, Parallelodon semicostatus, Modiola sp., Glauconome, 

 Fenestella sp., Betvpora pluma, Phill., Ghjphioccras spirale, Phill, sp., and Orthis 

 Micltelini. 



Sciiizodus oeovatus, M'Coy., sp., 1844. Plate XXIV, figs. 14, 15. 



Axinus obovatus, M'Coy, 1844. Syuops. Carb. Foss. Ireland, p. 64, pi. viii, fig. 30. 



Specific Characters. — Shell of medium size, obovate, moderately gibbose. The 

 anterior end rounded, the inferior border convex, the posterior obliquely truncate 



