2 CARBONIFEROUS LAMELLIBRANCHIATA. 



Pinna in^quicostata, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 86. 



— FLEXicosTATA, M'Coy, 1844. Ibid., p. 85, pi. xix, fig. 1. 



— FLABELLiPOBMis, Bronn, 1848. Noraencl. Palaeont., p. 978. 



— — Brown, 1849. Illust. Foss. Conch., p. 169, pi. Ixvii, 



fig. 19. 



— — d'Orbigny, 1850. Prodrome Paleont., vol. i, p. 135. 



— — Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 180. 



— FLEXICOSTATA, Morris, 1854. Ibid., p. 180. 



— FLABELLiFORMis, M'Coy, 1855. Brit. Pal. Foss., p. 498. 



— FLEXICOSTATA, M'Coy, 1855. Ibid., p. 499, pi. iiiE, figs. 11 — 18. 



— FLABELLIFORMIS, Griffith, 1860. J. Geol. Soc. Dublin, vol. ix, p. 93. 



— FLEXICOSTATA, Griffith, 1860. Ibid., p. 94. 



— iN^QUicosTATA, Griffith, 1860. Ibid., p. 94. 



— FLABELLIFORMIS, Eichivalcl, 1860. Lethsea Kossica, vol. i, p. 985, pi. 



xxxviii, fig. 23. 



— — Wardle, 1863. Sleigh's Ancient Hist. Leek, pi. iii, fig. 5. 



— — Young and Armstrong, 1871. Trans. Geol. Soc. Glasgow, 



vol. iii, suppl. p. 47. 



— — Armstrong, Young, and Robertson, 1876. Cat. West. 



Scott. Foss., p. 52. 



— FLEXicosTA, Armstrong, Yovng, and Robertson, 1876. Ibid., p. 52. 



— SPATULA, Roemer, 1876. Lethsea Palseoz. Atlas, taf. xliv, fig. 10. 



— FLABELLIFORMIS, Bigsby, 1878. Thesaurus Devonico-Carboniferus, p. 293. 



— FLEXICOSTATA, Bigsby, 1878. Ibid., p. 293. 



— FLABELLIFORMIS, fZe Kouinck, 1885. Ann. Mus. Roy. Hist. Nat. Belg., 



torn, xi, p. 164, pi. xxvii, figs, 1, 2. 



— — Etheridge, 1888. Brit. Foss., pt. i. Palaeozoic, p. 275. 

 cosTATA, Etheridge, 1888. Ibid., p. 275. 



— FLEXICOSTATA, Etheridge, 1888. Ibid., p. 275. 



— in.s:quicostata, Ethtridge, 1888. Ibid., p. 275. 



Sjjecific Characters. — Shell large, transverse, elongate, triangular, compressed. 

 The anterior end is obsolete, the inferior and superior borders almost meeting in 

 front. The inferior margin descends downwards and backwards, and is almost 

 straight ; the posterior margin is almost truncate, slightly convex. The hinge-lme 

 is long and straight. The umbones small, terminal and pointed, almost obsolete. 

 The valve is convex from above downwards, especially in front, but as the shell 

 expands posteriorly the convexity diminishes. 



Literior. — Casts of the interior show an elongate groove just below the superior 

 margin for the internal ligament, and a well-marked groove just Avithin the lower 

 border for its anterior third. The adductor scar is large and round, placed far 

 back on the dorsal slope. The internal surface above and below is smooth, but in 

 the median portion of the valve is marked by radiating, I'ounded folds and sulci. 



Exterior. — The surface is ornamented with radiating or subparallel ribs and 

 sulci, often exhibiting, some little distance from the anterior end, some slight degree 



