224 CARBONIFEROUS LAMELLIBRANCHIATA. 



the hinge has not been preserved. In fig. 9, PI. XVII, the posterior muscle-scar 

 seems to have been of extraordinary size and. strength, but all specimens do not 

 show it so well developed. This specimen is the largest example I have yet seen, 

 and is in the Woodwardian Museum, Cambridge. It shows some faint traces of 

 concentric markings near the lower margin. 



Schizodus antiquus, sp. nov. Plate XV11I, figs. 24 — 27 ; Plate XIX, figs. 4, 5. 



? CvriiEHiEA antiqua, Brown, 1841. Trans. Manch. Geo!. Soc, vol. i, p. 228, 



pi. vii, fig. 7G. 

 Anthracosia, sp., Wild, 1892. Trans. Manch. Geol. Soc, vol. xxi, p. 3G6, pi. ii, 



fig. 7. 

 Schizodus cahbonarius (pars), Ward, 1890. Trans. N. Staff*. Inst. Min. ami 



Mech. Engin., vol. x, p. 131. 

 — Salteiii, Barnes and Holroyd, 1897. Trans. Manch. Gcol. Soc, vol. 



xxv, pi., 1 fig. 12. 



Specific Characters. — Shell of moderate size, gibbose, ovate, quadrate, slightly 

 inequivalve. The anterior portion of the valve is much compressed, but soon 

 expands and becomes gibbose. The border is regularly rounded, it sweeps round 

 into the inferior margin, which is more gently convex and extended, terminating 

 abruptly where it meets the posterior border at a well-marked obtuse angle. The 

 posterior border is obliquely truncate from above downwards and straight. The 

 hinge-line is arcuate, and the postero-superior angle obtuse. The umbones are 

 gibbose, incurved, and somewhat elevated, situated a little in front of the middle 

 line. Proceeding backwards and downward towards the postero-iuferior angle 

 is a rounded oblique ridge, which gradually becomes less marked, but in large 

 specimens is continued to the very margin. In front of this ridge the valves are 

 evenly convex, but behind it the shell is rapidly compressed and somewhat 

 expanded, forming the dorsal slope. 



Interior. — The muscle-scars appear to be normal in position, and the pallia! 

 line entire, but somewhat remote from the border. Indications only of the hinge 

 are seen in one of the specimens, a cast, but little can be stated of it precisely. 



Exterior. — The surface is smooth, but the microscope reveals fine concentric 

 lines, especially near the margins. Shell thin. 



Dimensions. — Fig. 27, PI. XVIII, measures — 



Antero-posteriorly . . . .26 mm. 



Dorso-ventrally . . . .21 mm. 



Elevation of valve . . . .5 mm. 



Localities. — England : the Black Shales below the Millstone-grit of High 

 1 In this paper the plates bear no number. The Plate is the third in the paper. 



