74 CARBONIFEROUS LAMELLIBRANCHIATA. 



Palaeozoic Fossils,' p. 493, pi. iii/, fig. 2, is evidently not correctly referred to this 

 genus (vide antea, p. 72). 



LiTHODOMUS LiNGUALis, Phillips, 1836. Plate I, figs. 3, 4, 4 a, 5. Plate II, 



figs.l — 4. 



MoDiOLA LINGUALIS, PliilUps, 183G. Geology Yorkshire, part 2, p. 209, pi. v, 



fig. 21. 



— — Morris, 1843. Catal. British Fossils, p. 91. 



— — irCoy, 1844. Syuops. Carbonif. Fossils Ireland, p. 74. 

 LiTHODOMirs DACTTLOiBEs, M'Coy, 1844. Ibid., p. 75, pi. xi, fig. 41. 



MoDioLA LINGUALIS, Broiort, 1849. Illustrat. Fossil Conchology, p. 173, pi. Ixxii, 



fig. 42. 

 MxTiLUS LINGUALIS, d'OrUgny, 1850. Prodrome Paleontol., vol. i, p. 135. 

 MODIOLA LINGUALIS, Wardle, 1862. Sleigh's Ancient History of Leek, pi. iii, 



fig.C. 

 LiTHODOMUS DACTTLOIDES, Huxley and Etlieridrje, 1865. Cat. Foss. Pract. Greol., 



p. 110. 

 LiTHOPHAGA? LINGUALIS, Meeh and Wovthen, 1868. Geol. Survey Illinois, vol. iii, 



p. 536, pi. xix, figs. 1 and 2. 

 MoDiOLA LiTHODOMOiDES (pars), B. Etheridge, jun., 1875. G-eolog. Mag., dec. 2, 



vol. ii, p. 241, pi. viii, fig. 1. 



— PEiNCEPS, de Koninch, 1885. Ann. Musee E. Hist. Nat. Belg., vol. xi, 



p. 174, pi. xxviii, fig. 3. 



— rusiroEMis, de Koninck, 1885. Ibid., figs. 2, 4—7, 29, and 30. 



— LINGUALIS, R. Etheridge. Brit. Foss., vol. i, Palseozoic, p. 285. 



— LITHODOMOIDES, B. Etheridge. Ibid., p. 285. 

 LiTHODOMUS DACTTLOIDES, B. Etheridge. Ibid., p. 284. 



Non MoDiOLA LITHODOMOIDES, Ward, 1890. Trans. N. Staff". Inst. Min. and Mech. 



Engineers, vol. x, p. 130, pi. i, fig. 11. 



Specijic Characters. — Shell very transversely elongated and slightly oblique, cylin- 

 drically flattened from side to side in front, but expanded and flattened posteriorly. 

 The anterior extremity is bluntly pointed and narrow, somewhat flattened towards 

 the ventral margin, but convex above. The ventral margin is convex at the anterior 

 and posterior thirds, but slightly concave in the middle third. The posterior 

 margin is formed by two convex lines meeting at an angle at a point a little 

 below the centre, the upper part having a wider and longer sweep than the lower. 

 The hinge-line is straight, and slightly longer than one-half the extreme length 

 of the shell, and passes into the posterior border almost impercej)tibly. The umbones 

 are small and inconspicuous, obtuse, non-contiguous, very anterior, but not quite 

 terminal, not well defined from the rest of the shell in front. The valves are 

 regularly swollen in front, the greatest gibbosity being nearer the upper than the 

 lower border. The swelling is slightly oblique and diminishes, but at the same time 



