ANTHRACOMYA SENEX. Ill 



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, Adclerley Green, Longton. 



Observations. — 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. Anthracomya senex, Salter. Plate XV, figs. 21 — 28. 



Anthracomya senex, Salter. " Iron Ores of South Wales," Mem. of the Geol. 



Surv., 1861, p. 230, pi. ii, fig. 10. 

 — — Hind. Quart. Journ. Geol. Soe., 1S93, pi. s, p. 270, 



figs. 20, 20 «, 21. 



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 



