120 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 
I noted in my first description that this shell somewhat resembled Anthracomya 
lanceolata, Pl. XV, fig. 11. It may be that this form stands in the same relation 
to A. Williamsoni that the variety A. carinata does to A. minima ; and I am the 
more inclined to think that this is the case, as I meet with an elongate form of 
Anthracomya pulchra, Pl. XV, fig. 29, and an elongate form of Anthracomya 
Adamsii, Pl. XII, fig. 9, each occurring and only occurring in the same beds as the 
normal variety, though this may not be true of A. Williamsoni and the form A. 
lanceolata, as the actual horizon at which the latter occurs is at present uncertain. 
14. AnrHracomya Puiturrsu. Plate XVI, figs. 10—16. 
Unio Pariiiesi, Williamson. Phil. Mag., vol. ix, p. 351, 1886. 
Non — utyeurrormis, Phillips. Murchison’s Sil. Syst., p. 88, 1839. 
Moprota, sp., Binney. Mem. Lit. Phil. Soc. Manchester, 2nd ser., vol. xii, p. 221, 
note, 1855. 
Anturacomya Puinirpsi, Hualey and Etheridge. Cat. Foss. Mus. Pract. Geol., 
pp. 157—160, 1865. 
— _— T. Rupert Jones. Geol. Mag., vol. vii, p. 217, pl. ix, 
figs. 3 and 18, 1870. 
_ — R. Etheridge, jun. Ibid., ser. 2, vol. iv, pp. 248, 244, 
pl. xu, figs. 6 and 7, 1877. 
= = Hind. Quart. Journ. Geol. Soc., vol. xlix, 1893, p. 262, 
pl. ix, figs. 6, 6a, 7, 8; pl. x, fig. 27. 
Specific Characters.—Shell transversely obliquely oval, modioliform, elongated 
in a diagonal direction. The anterior end is small, its margin rounded. The 
posterior end is compressed, expanded downwards and backwards, while above it 
is rapidly compressed into the upper border, which is elevated posteriorly. The 
hinge-line is straight, about one-half the length of the diagonal of the shell. The 
ventral margin is convex, passing with a gentle curve into the anterior end, and 
becoming straight shortly before it reaches the posterior end. The umbones are 
anterior and directed forwards, very blunt and gibbose, the beaks themselves 
inconspicuous. The shell itself is fairly tumid, and the valves are gibbose. ‘There 
is no sign of an oblique constriction anterior to the gibbosity, which is itself very 
gradual in its form. Behind the gibbosity the valves are so rapidly compressed 
as to become hollow on the posterior slope. 
Interior.—As far as can be seen in Pl. XVI, fig. 14, which is a cast, the interior 
is normal, but the anterior adductor scars are not seen, owing to damage to the 
specimen. 
EHxterior.—The surface is covered by fine and coarse striz and lines of growth, 
which have the general arrangement which obtains in this genus. Periostracum 
thick and wrinkled. 
