ANTHRACOMYA WILLIAMSONI. 99 
antero-posteriorly, its greatest dorso-ventral measurement (towards the posterior 
end) is 32 mm., and 22 mm. from side to side: this specimen is more typical in 
shape than the one figured. I noted also in the Museum at Brussels a large 
example measuring 54 mm. from before backwards, from the Coal-measures of 
Longchamps, but have not met with the form in other Continental museums. 
4, AnrHracomya WILLIAMSoNI (Brown). Plate XIV, figs. 12—31; Plate XV, fig. 10. 
P AnoponTa TENERA, Hichwald. Urwelt Russlands, p. 101, pl. iv, figs. 2,3, and 4, 1840. 
? Myvritus (Moprona) TEpiori, de Vernewil. Géol. de la Russie, vol. ii, p. 318, 
pl. xix, fig. 17, 1845. 
_ PREPES, de Ryckholt. Mélanges Paléontologiques, p. 158, le part, 
pl. viii, figs. 1, 2, 1848. 
Moprora WitiiaMsont, Brown. Fossil Conchology, pl. Ixxi, figs. 24, 25, p. 172, 
1849. 
MoproLopsis TENERA, Hichwald. Letha Rossica, p. 977, pl. xxxix, fig. 4, 1855-9. 
— TepLori, Hichwald. Ibid., p. 978, 1855-9. 
ANTHRACOMYA SANGUINOLARIS, Salter. Memoirs of the Geological Survey of 
Great Britain, “The Geology of the 
Country around Bolton-le-Moors,” 
p- 35 (no description or figure), 1862. 
ANODONTA TENERA, Ludwig. Pal. Urals; Paleontographica, vol. x, p. 20, pl. iii, 
fig. 13, 1863. 
Anrturacosta WEIsstana, Geinitz. N. Jahrbuch fiir Mineralogie, &c., 1867, p. 682. 
PLEUROPHORUS suBCosTaTUS, Meek and Worthen. Geol. Sury. Illinois, vol. ii, 
: p- 347, pl. xxvii, figs. 2,2 a, 1866. 
ANTHRACOSIA BILBoENSIs, Kinahan. Geol. of Ireland, pl. iv, fig. 5, 1878. 
— _ Baily. Geol. Surv. Ireland, Exp. of Sheet 137, p.12, 1859. 
_- Harz, Achepol. Niederrheinisch- Westfalische Steinkohlen-Gebirge, 
Atlas, p. 109, Supplement ii, figs. 8 and 9, 
1880—1883. 
ANTHRACOMYA ELONGATA, Hind. Quart. Journ. Geol. Soe., vol. xlix, p. 266, pl. x, 
figs. 1—12, 1893. 
Specific Characters.—Shell very transversely elongate, very inequilateral, wedge- 
shaped, and compressed. ‘The anterior end is small, narrow from side to side and 
above downwards, with an acutely rounded border, which passes downward 
rapidly into the inferior border, and forms above a blunted right angle with the 
hinge-line. The posterior end is expanded and produced, and is gradually 
compressed into its borders, but much more rapidly so upwards into the 
hinge-line. The inferior border is nearly straight, but is slightly sinuated about 
its centre. The posterior border is truncate, with the upper and lower angles 
more or.less rounded. The hinge-line is straight, raised, and compressed 
