222 CARBONIFEROUS LAMELLIBRANCHTATA. 



species is at once distinguished from the other Carboniferous forms by its pro- 

 duced and bluntly pointed posterior end, and by the regularity of its lines of 

 growth. 



It is probable that Young and Armstrong referred the name Axinus axini- 

 formis to quite a different shell; as, from what I can observe, the species is rare 

 in the West of Scotland. 



Schizodus carbonari us, Soiverby, sp., 1840. Plate XVII, figs 7 — 0. 



Venus? caebonaeia, Sowerby, 1840. Geol. Coalbrookdale, pi. xxxix, tig. 2. 

 .Noil — — (ampiiidesma), Fortlock, 1813. Eep. Geol. Londonderry, 



p. 438, pi. xxxvi, fig. 8. 

 Ampiiidesma caebonaeia, Morris, 1813. Cat. Brit. Foss., p. 77. 



— caebonaeiuh, Broivn, 1819. Illust. Foss. Concli., p. 221, pi. xci, figs. 



44, 45. 

 Axinus cabbonaeius, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 189. 

 Non Myophoeia caebonaeia, M'Coy, 1855. Brit. Pal. Foss., p. 495. 



Scmzc-Dus caebonaeius, Salter, 1861. Mem. Geol. Surv. Gt. Brit., Iron Ores Gt. 



Brit., pt. 3, p. 221, [>1. i, fig. 30. 

 Non Axinus cabbonakius, Young and Armstrong, 1871. Trans. Geol. Soe. Glasg., 



vol. iii, Appendix, p. 50. 

 — — — 1876. Cat. West-Scottish Foss., 



p. 53. 

 Sciuzonus caebonaeius (pars), R. Etheridge, 1888. Brit. Foss., vol. i, Palaeozoic, 



p. 290. 



Specific Characters. — Shell subquadrate, gibbose, inequilateral. The anterior 

 portion is regularly swollen, its upper part compressed backwards and flattened 

 to form an anterior surface, cordate in shape, bounded on each side by the 

 anterior umbonal ridge, and slightly elevated in the middle line where the anterior 

 margin of the valves projects forwards. The anterior border is regularly and 

 convexly curved, passing into the hinge-line above and inferior border below 

 without any break. The iuferior border is convex downwards, the segment of a 

 larger curve than that which forms the anterior edge of the valve. The posterior 

 border is truncate, nearly straight, and slightly obliquely inclined from above 

 downwards, making an obtuse angle with the hinge-line above and the inferior 

 border below. The hinge-line is short, especially in front, and almost straight. 

 The umbones are prominent, swollen, incurved, non-contiguous, raised above the 

 hinge-line, and situated about the junction of the anterior and middle thirds of 

 the valve. The anterior surface of the umbo is flattened, and from the posterior 

 edge a bluntly rounded oblique ridge descends to the postero-inferior angle, 

 which marks off the posterior slope from the rest of the valve. The lateral 



