220 CARBONIFEROUS LAMELLIBRANCHIATA. 



Non Amphidesma axiniformis, For/lock, 1S43. Geol. Londonderry, p. 439, pi. xxxvi, 



fig. 6. 

 Non — — Morris, 1843. Cat. Brit. Foss., 1st edit., p. 77. 



Axinus sulcatus, Morris, 1843. Ibid., p. 80. 



Isocardia axiniformis, Morris, 1843. Ibid., p. 88. 



Cardiomorpha axiniformis, M'Cog, 1843. Carb. Foss. Ireland, p. 56. 

 Non Axinus axiniformis, M'Coy, 1843. Ibid., p. 03. 



— obscurus ?, Brown, 1840. Illust. Foss. Conch., p. 194. pi. lxxix, figs. 5, 0, 7. 

 Isocardia axiniformis, Brown, 1849. Ibid., p. 197, pi. lxxx, fig. 0. 

 Cardiomorpha axiniformis, d'Orbigny, 1850. Prodrome de Paleont., p. 133. 

 Axinus axinifoemis, Morris, 1854. Cat. Brit. Foss., 2nd edit., 1854, p. 1S8. 



— sulcatus, Morris, 1854. Ibid., p. 189. 



? Sciiizodus Chesterensis, Meek and Wbrthen, 18G5. Proc. Acad. Nat. Sci. 



Phil., p. 457 ; Geol. Surv. Illinois, PalseontoL, vol. ii 

 p. 301, pi. xxiii, figs. Ga, b. 

 ? Axinus axiniformis, Young and Armstrong, 1871. Trans. Geol. Soc. Glasg., 



vol. iii, Appendix, p. 49. 

 ? — — — 1S7G. Cat. AVest- Scottish Fossils, 



p. 53. 

 Sciiizodus sulcatus, Barrois, 1882. lvccherch. sur les Terr. Anciens des 



Asturias et de la Galice, p. 340. 



— axiniformis, B. Etheridge, 1885. Brit. Foss., vol. i, Pal. p. 290. 



— sulcatus, B. Etheridge, 18S5. Ibid. 



Specific Characters. — Subtriangularly ovate, transversely produced, gibbose, 

 inequilateral. The anterior end of the shell is generally convex below, but above 

 it is compressed backwards into the uinbones, and flattened, forming a cordate 

 anterior surface, which is separated from the lateral surface of the valve by a 

 rounded angular ridge, from the centre of which the prominent and raised 

 anterior border projects. This border is elliptical, and it passes above and below 

 into the hinge-line and lower border respectively Avithout interruption. The 

 inferior border is regularly but gently curved, with the convexity downwards. 

 The posterior end is obtusely pointed, and its border obliquely truncated from 

 above downwards, joining the lower border at a more or less marked acute angle. 

 The hinge-line is short, curved, and its extent ill-defined. 



The umbones are gibbose anterior to the middle line of the valve, elevated 

 above the hinge-line, pointed, incurved, and directed forwards, non-contiguous, 

 with an angulated border in front continuous with the outer edge of the anterior 

 surface. Behind, the posterior border of the umbo is continued downwards as a 

 rounded ridge to the postero-inferior angle; above this line the dorsal slope is 

 depressed, compressed, and hollowed, so as to be concave in transverse section. 



Interior. — The anterior adductor muscle-scar is oval, shallow and incon- 

 spicuous, and close to the margin. The posterior adductor scar is deeper, ovate, 

 and situated in the hollow of the dorsal slope near the junction of the hinge-line 



