ANTHRACOMYA SENEX. lil 
expanded, flattened backward and downward, and into the hinge-line, which is 
much raised. The hinge-line is straight, about three-quarters the length of the 
shell. Umbones prominent, blunt, separate, situated one-seventh the distance of 
the hinge-line from the anterior end. The inferior border is curved rapidly 
downward from the anterior end, then becomes bluntly and gently rounded into 
the posterior border, which extends in the form of a regular semicircular curve 
from the inferior to the superior angle. A blunt swelling, rapidly flattened on its 
posterior side, extends from the umbo to a point in the inferior border anterior to 
its posterior limit. There is no appreciable byssal sulcus, but there appears to 
have been a byssal notch at the junction of the anterior and middle thirds of the 
inferior border. 
Interior smooth, with folds of growth; anterior and posterior adductor scars 
as in other species. Ligament external. Lunule distinct. 
Measurement.—Antero-posterior measurement 30 mm.; greatest dorso-ventral 
(at posterior end) 17 mm.; from side to side 7 mm. 
Locality.—Roof of the Hard-mine Coal, Adderley Green, Longton. 
Obserrations.—I have found only one specimen of this very distinct and 
characteristic form. It looks much like some forms of Anthracoptera, from which 
it can be distinguished by its umbones and hinge-line. It has occurred to me 
that this may well be an example of mimicry, the more so because the form 
Naiadites elongata resembles very closely certain forms of Anthracomya ; in fact, it 
is only on very close examination of the umbones and hinge-lines that these forms 
can be correctly referred to their proper genera. 
The fact that I have only been able to obtain one good example of this species 
throws some doubt as to its reality, and it is quite possible that the shell may be 
a deformity or even a hybrid. The expanded posterior end and anterior position 
of the umbones indicate an approach towards the form of A. senex, but there is 
no pronounced angularity of the diagonal ridge. 
10. AnraRracomya sHNEX, Salter. Plate XV, figs. 21—28. 
“Tron Ores of South Wales,’ Mem. of the Geol. 
Surv., 1861, p. 230, pl. i, fig. 10. 
— — Hind. Quart. Journ. Geol. Soc., 1893, pl. x, p. 270, 
figs. 20, 20 a, 21. 
ANTHRACOMYA SENEX, Salter. 
Specific Characters.—Shell transversely cuneiform, oblique, moderately convex. 
The anterior end is small, ellipsoidal, and blunt, and the narrowest part of the 
shell. Its border is regularly curved, and passes gradually into the inferior 
border, which is directed downwards and backwards, being slightly sinuated about 
its centre. The posterior border is obliquely truncate from above downwards and 
