ANTHRACOMYA DOLABRATA. 93 



2. Anthracomya dolabrata (Soiverby). Plate XIII, figs. 4 — 9 and 11. 



Unto dolabratus, Sowerb//. Traus. Geol. Soc, ser. 2, vol. v, pt. 3, 1840, pl.xxxix, 



fig. 9. 

 — Brown. Foss. Conch., 1849, pi. lxxxviii, fig. 17. 



Anthracomya dolabrata, Salter. Geol. Surv. Mem. Iron Ores of S. Wales, 



1861, p. 230, no fig. 

 — — Hind. Quart. Journ. Geol. Soc, p. 261, pi. viii, 



1893, figs. 9, 9«, 10« ; pi. ix, figs. 1, 1 a. 

 ]N"on — — — Ibid., pi. ix, figs. 4 and 5. 



Specific Characters. — Shell tumid, subquadrate, transversely elongated and 

 expanded upwards posteriorly. The anterior end is short, compressed, and 

 comparatively narrow, its upper border being far below the umbones. The 

 border is sharp and bluntly rounded, passing insensibly below into the lower 

 border, which is rapidly produced downwards and backwards, being almost 

 straight at first, but becoming bluntly rounded into the posterior border behind. 

 The posterior border is obliquely truncate in its upper part from above downwards, 

 rounded below. The hinge-line is straight, much raised posteriorly, equal to 

 about five-sixths of the lenp-th of the shell in extent. The umbones are obtuse 



o 



and gibbose, raised above the hinge-line, contiguous, situated at a distance equal 

 to about one-third of the length of the hinge-line from the anterior end. The 

 lunule is long and narrow, the shell is obliquely swollen, the tumidity being 

 continuous with the umbones, and gradually rounded off both in front and behind. 

 Just anterior to the swelling is a very shallow depression, which becomes wider as 

 it progresses towards the lower margin. Posterior to the swelling the shell is 

 gradually and regularly compressed into the border, particularly so above, to such 

 an extent that the posterior slope of the shell is concave. The tumidity is most 

 developed above the widest part of the shell, being just below the level of the 

 hinge-line ; downwards and backwards the swelling gradually becomes less, but it 

 can be traced to the inferior margin some little way anterior to the posterior 

 inferior angle. 



The interior has not yet been exposed. 



Exterior. — The shell is ornamented by fine striae and lines of growth, which, 

 crowded in front, become slightly separated as they pass backwards over the shell, 

 and on reaching the oblique swelling they become deflected upwards to terminate 

 in the superior border. Periostracum thin and wrinkled. 



The ligament is external and small, but erect, equal in length to about one- 

 fourth the length of the hinge-line. Posterior to the ligament there is a shallow, 



