132 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 
Myrinus WeseMantianus, de Ryckholt. Mélanges paléontologiques; Mém. 
Couronn. Acad. Roy. Belg.,vol. xxiv, 
1852, p. 140, pl. viii, figs. 11, 12. 
Moprota Wyominaensis, Lea. Journ. Acad. Nat. Sci. Philad., new ser., vol. 1, 
pt. 3, p. 203, pl. xx, fig. 1 a, 1853. 
Dreissenta Lacrniosa, &. Ludwig.  Paleontographica, vol. viii, p. 38, pl. v, 
figs. 15, 19, 1859. 
= inFuaTa, PR. Ludwig. Ibid., vol. viii, p. 190, pl. 1xxi, figs. 8—10, 1861. 
a DILATATA (pars), &. Ludwig. Ibid., p. 189, pl. xxi, figs. 5—7. 
Myatina mopronarts, Salter. Geol. Surv. Mem., ‘Iron Ores of South Wales,’ 
p. 228, pl. ui, fig. 14, 1861. 
AntHRacoMya? mopronaris, Salter. Ibid., p. 230, pl. ii, fig. 14. 
— = Ward. Trans. North Staff. Inst. Min. and Mech. 
Engin., vol. x, 1890, p. 125, pl. i, fig. 13, 
1890. 
ANTHRACOPTERA MODIOLARIS, Hind. Quart. Journ. Geol. Soc., vol. xlix, p. 251, 
vol. vil, figs. 1, 1 a, 16, 3—6, 1893. 
Specific Characters.—Shell obliquely elongated, compressed posteriorly. The 
hinge-line is straight, nearly or quite as long as the greatest length of the shell. 
The anterior part of the shell is represented by a small gibbose lobe, which 
projects forwards with a rounded border, which becomes concave below, and is 
pierced by the byssus. The posterior part forms the greater portion of the shell; 
it is produced downwards and backwards, expanded, and gradually compressed into 
the margin. The posterior border is bluntly curved, but it may be straight or 
even emarginate, and meets the hinge-line at an angle which is either greater than 
or equal to a right angle. The junction of the inferior and posterior borders is 
bluntly curved. The umbones are anterior, not quite terminal, and on reaching 
the hinge-line are curved forwards and inwards, not contiguous, slightly elevated 
above the hinge-line. An acute and prominently swollen ridge, flatter in young 
specimens, passes obliquely backwards and downwards, and, while preserving its 
character in the anterior two-thirds, rapidly becomes lost in the lower and poste- 
rior third. Anterior to this oblique ridge the shell is markedly constricted, often 
becoming slightly concave. The ridge is bent forwards in front, and is parallel to 
the hinge-line. It is much more pronounced in the left valve. The right valve is 
much flattened. 
Interior.—The anterior muscle-scars are three in number, pit-like ; the anterior 
markedly the largest, and situated within the umbo; the next is situated 
just below the horizontal part of the ridge (in casts), while the posterior scar 
is on the right exactly at the point where its direction becomes changed 
downward. ‘The posterior scar is large and obovate, situated close to the 
posterior superior angle of the shell. Faint traces of the attachment of byssal 
muscles are occasionally seen near the upper border. Two or three slight 
