112 CARBONIFEROUS LAMELLIBRANCHIATA. 



Ironstone, and the Geological Surveyors in the 'Memoirs on the Geology of 

 Plashetts and Kielder,' and the ' Geology of the Country round Otterburn and 

 Elsdon ' mention Myalina crassa, M. Vemeuilii, M. lamellosa, and M., sp., from 

 beds of the same age. It appears to me probable that fragments of the shell 

 under description may have been mistaken for M. Flemingi, M. crassa, and 

 possibly the others. 



Miss Jane Donald has obtained specimens from a bed of arenaceous limestone of 

 the Yoredale series of Garsdale. One, which I am allowed to figure, PI. V, fig. 1, 

 though compressed, shows very beautifully the condition of the upper and 

 posterior angle of the shell, and the sinuously curved border with a similar curvature 

 in the lines of growth just below their termination in the hinge-line. 



Myalina Flemingi, M'Coy, sp., 1844. Plate IV, figs. 9, 10, 10 a, 10 6. 



Mytilus Flemingi, M'Coy, 1844. Synops. Charact. Carboniferous Foss. Ireland, 



p. 76, pi. xi, fig. 29. 

 ? — comptus, M'Coy, 1844. Ibid., p. 76, pi. xiii, fig. 12. 



— Beaumonti, de Verneuil, 1854. Geol. de la Russie d'Europe, vol. ii, 



p. 315, pi. xxii, fig. 2 a, b. 



— Flemingii, Morris, 1854. Catal. Brit. Foss., 2nd edit., p. 214. 



— — Bigsby, 1875. Thesaurus Devonico-Carboniferus, p. 309. 



— — Etheridge, 1886. Brit. Foss., vol. i, Palseoz., p. 287. 



— ? Flemingi, de Koninck, 1885. Faune Calc. Carbonif. Belg., p. 180. 

 Mytilahca Flemingi, de Koninck, 1885. Ibid., pi. xxix, figs. 22, 26 — 28. 



Specific Characters. — Shell of very moderate size, obliquely trigonal, keeled. 

 The anterior end is obsolete, but the shell has a marked anterior surface, which is 

 ovate-lanceolate in shape, slightly convex from side to side, above flat or slightly 

 concave towards the centre, and again convex to a very small extent below. The 

 margins of this surface are acutely angulated, especially on the right side, and, 

 starting at the umbones, at first are directed outwards at a right angle, then 

 they become arched downwards, still in an outward direction, till the centre of the 

 shell is reached, when they gradually approximate and join in the anterior part of 

 the lower border. The anterior surface is placed at an angle of about 45° with the 

 hinge-line. The inferior border is bluntly curved, and is formed in front by the 

 gradual version of the extreme edges of the valve, which become slightly 

 elevated in the centre of the anterior surface. This border is somewhat angulated 

 where it meets the posterior border, which is obliquely truncate or very slightly 

 convex in outline, and has a general direction parallel to the anterior surface. 

 The hinge-line is almost as long as the greatest antero-posterior horizontal 



