FOSSILS OF NEW SOUTH WALES. 693 
name was already used in the science,) has the following characters, as derived from two 
species in our collections, the P. antiquatus and P. cuneatus. 
Equivalve, inequilateral, more or less oblong, thick, closed. Beaks moderately promi- 
nent. Exterior with coarse irregular concentric ridges. Lateral surface a little flattened, 
and inferior margin straight at middle, or slightly excavate. Ligament large, external. 
Palleal impression entire, strong and broad, reaching quite to the larger anterior mus- 
cular impression. Muscular impressions three to each valve, two anterior strongly exca- 
vate, posterior less so. Smaller anterior, situated under the beaks, and the muscle 
having a direction inward (the impression of a cast facing frontwise or inward). Larger 
anterior broad, with the upper border broad truncate. Posterior, large and rounded, sub- 
quadrate. Cast having the beaks distant; cardinal area broad and long, and with a 
carinate border ; posterior muscular impression situated on the broad flank, and its inner 
angle produced forward, and extending over the carina; lateral surface, from the beak 
obliquely downward, flattened or concave. On the surface of the cast there are several 
small elevated points, which appear to mark attachments of muscular fibres. The valves 
are thin just anterior to the middle, and thicken towards the margin. 
The genus is near Crassatella, Astarte, Astartila, Cardinia, and Maonia. 'The last 
four genera have the same number of muscular impressions, but Meeonia is peculiar in 
the smaller anterior muscular impression having the same lateral direction as the larger 
anterior, instead of being directed forward or inward, and the large anterior muscular im- 
pression being subacute above instead of broad truncate. The specimens resemble most, in 
their casts, the species referred to Cardinia; but the latter are very much elongated, and 
have a long linear cardinal area to the cast, and are almost without a beak to the shell, as 
well as to the cast; moreover, the upper side of the larger anterior muscular impression 
is not horizontally truncate as in’ Pachydomus, In Astartz/a, the larger anterior impres- 
sion, besides differing in form, is oblong in the direction of the striz, and the palleal im- 
pression has a gradual curve, instead of the rather abrupt bend posteriorly which charac- 
terizes Pachydomus and Meonia; the general form, and small cardinal area to cast, are 
also different. 
32, Pacuypomus cungatus (J. D. Sowerby), Morris——From Harper’s Hill, valley 
of the Hunter.—Plate 5, fig. 1, 1 a, views of cast, natural size.—Length of cast 22 
inches ; height 77°, L. ; thickness °°, L.; height of shell (from Mitchell’s figure) 5°95 
The cardinal area in the cast is very broad ; it narrows abruptly at the upper part of 
the posterior muscular impression, where there is an angle in the carina. The beaks are 
very distant. The flanks are flattened, the posterior muscular impression is large quadrate, 
and covers the full breadth of the flank. The palleal impression is hardly half an inch 
from the lower margin; it is broad and strong, with the surface a little undulate. The 
large anterior muscular impression is vertically oblong, and deeply excavate. This species 
is much more oblong than the following, and is peculiar in its truncate front, and the 
angle over the upper part of the posterior muscular impression ; also in the lower margin 
being somewhat excavate. 
Megadesmus cuneatus, J. D. Sowerby, Mitchell’s Expeditions into Australia, 8vo. London, 
1838, vol.i., pl. 3, fig. 3. 
Pachydomus cuneatus—J. Morris, in Strzelecki’s New South Wales, p. 272. 
33. Pacnypomus antiquatus (J. D. Sowerby), Morris——From Harper’s Hill.— 
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