422 CARBONIFEROUS LAMELLTBRANCHTATA. 



Alldimsma sulcata, Fleming, sp., 1828. Plate XLVIII, figs. 3 — 11. 



TTiATELLA SULCATA (pars), Fleviiiif/, 1828. Hist. Brit. Aniin., p. 462. 

 Venus ellutica, Phillips, 1836. Geol. Y'ork., pt. ii, p. 109, pi. v, fig. 7. 

 PosiDONOMYA TRANSTEBSA, Portlock, 1848. Geol. Eep. Londonderry, p. 745, 



pi. xxxviii, fig. 9. 

 Allokisma sulcata, King, 1819. Monogr. Perm. Foss., in foot-note, p. 198. 

 IMtacites sulcata, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 213. 

 vSanguinolites sulcatus, M'Coy, 1855. Brit. Pal. Foss., p. 507. 

 MvACiTES sulcata, Salter, 1861. Mem. Geol. Surv. Gt. Brit. Iron Ores, pt. 3, 



p. 221, pi. i, fig. 28. 

 Allorisma sulcata, Bigshy, 1877. Thesaurus Devonico-Carboniferus, p. 295. 

 — — Etheridf/e, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 277. 



Specific Characters. — Shell of only medium size, transversely oblong, moderately 

 gibbose, very inequilateral, gaping slightly behind. The anterior end is short, 

 only projecting a little in front of the umbones, gradually compressed, narrowed 

 from above downw^ards at the expense of its antero-superior part ; its margin 

 regularly rounded, passing with a continuous curve into the inferior border, which 

 is only slightly convex as a whole, and distinctly sinuous, in front of its middle 

 point. The convexity increases posteriorly, and passes gradually into the regularly 

 but bluntly curved posterior border, which makes a more or less well-marked 

 obtuse angle with the hinge-line. The upper border is somewhat shorter than 

 the tra,nsverse diameter of the valve. It is much arched in front, but is straight 

 posteriorly, and may even be slightly elevated at the extreme postero-superior 

 angle. The umbones arc small, gibbose, hardly raised, pointed, curved inwards 

 and forwards, and placed far forwards. The lunule is elongate and depressed, 

 excavating the umbones anteriorly. The escutcheon is long, deep, and narrow, 

 bounded externally by a slightly curved, elevated, angular ridge, which separates 

 the escutcheon from the dorsal slope. 



The valves are convex in the umbonal region, and become compressed 

 gradually towards the margins. There is a well-marked compression which passes 

 from below the umbones to the inferior margin, becoming broader and deep, and 

 making the inferior margin somewhat sinuous. The dorsal slopes are compressed, 

 especially immediately below the erect dorsal margin, where there is an elongate 

 groove, which passes from the umbonal region to the postero-superior angle. 

 Proceeding downwards and backwards from the umbones to the postero-inferior 

 angle is a very obscure, almost obsolete, rounded ridge ; an obscure curved ridge 

 also passes from the umbo downwards and forwards across the upper part of the 

 anterior portion of the valve to the anterior margin. 



Interior. — The anterior adductor muscle-scar is round and shallow ; the 



