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other ; the larger, which is usually closest to the ventral margin, is generally 
reniform, which the smaller is suh-orbicular. A very much smaller impression 
than the preceding, probably that of the foot, is seen just behind the beaks, 
very close to the hinge line. 
delations and Differences. — This species, capable of attaining a great 
size, resembles, in general form and ornamentations, the genus Inoceraiims, 
a genus to which McCoy referred the species described by him, referring it 
to this genus only until its characteristics were better known. It differs 
from Inoceramus by its muscular impressions and hinge area ; the same 
characteristics distinguish it from Amhonycliia, J. Hall, which includes 
some species often confounded with Inoceramus, e.g., A. veiusta, Sowerby ; 
the right valves of Ambongcliia possess a small anterior ear, of which 
Aphanaia have no trace. So far this genus has only two species, of both of 
which I give descriptions, and one of them was known as early as 1817. They 
both belong to the Carboniferous System of Australia, and were found by the 
Hev. W. B. Clarke. It is remarkable that the Palaeozoic rocks of America 
and Europe, the fauna of which is much richer in species than that of 
Australia, should have furnished nothing that can be compared to these. 
Genus — APHANAIA. 
Aphanaia Mitchellii, F. McCoy. 
PI. XXI, Pig. 5. 
Inoceramus Mitchellii, p. McCoy, 1817, Ann. Mag. Xat. Hist., XX, p. 299, ])!. 14, fig. 1. 
This is an oval, slightly oblique, and slightly gibbous shell, of very 
large size. Its left valve is a trifle smaller than the right. The hinge line is 
straight, and shorter than the longitudinal diameter of the shell. The beaks 
are anterior, recurved, and pointed; the posterior margin is arched, the 
anterior margin is nearly rectilinear, forming a right angle with the hinge 
line, and united to the sub-semicircular ventral margin by a curve. The 
surface is ornamented with a greater or smaller number of irregular undula- 
tions of growth. The shell of this species has not been found. The muscular 
impressions are remarkable and quite distinct, although superficial; they 
consist, first of a double impression produced by the adductors, and a smaller 
one, probably that of the retractor of the foot, behind the beaks and close to 
