240 
tlie hinge line. Of the two first, which are placed near the middle of the 
valves and not far from the posterior margin, one is much larger than the 
other, the first is nearly circular, while the second, which is double its size, is 
suh-semilunar and curves round a part of the first (PI. XXI, Pig. 5a). 
The small impression of the muscle of the foot appears to he double, and 
more deeply hollowed in the valve than the preceding. 
Dimensions . — These are very variable ; those given here are taken 
from a specimen wdth one j)erfectly-preserved valve : — length six, breadth 
seven, thickness about three, length of hinge line three and a half centimetres. 
Horizon and Localities . — According to McCoy this species is abundant 
in the sandstone at Glendon and Wollongong. Mr. Clarke found it in the 
sandstone at Muree and Branxton. 
Apeanata gigantea, L. G. de Koninck. 
PI. XXI, Pig. 6. 
This is a very large, transversely oblique, oval, pointed shell. Its right 
valve is very much thicker, and a little larger than the left ; the former is 
recurved on itself by the turning up of the ventral margin. The beaks are 
thick, nearly straight, pointed and terminal. The hinge line is straight and 
very oblique with reference to the direction of the beaks. The surface 
exhibits very large, irregular, concentric undulations. Judging from some 
traces of it the test was very thin, the hinge alone is formed of a pretty thick, 
rounded callosity. The impressions of the adductor muscles are enormous, 
and are placed betv/een the posterior and ventral sides of the shell not far 
from the margins ; one is oval, and only half the size of the other, although 
its greatest diameter may be three centimetres ; it projects a little into the 
second which, except for the hollow'' produced by the first, would also be oval 
and have a diameter of five and a half centimetres. The impression of the 
muscle of the foot is minute, scarcely perceptible, and placed near the middle 
of, at a short distance from, the hinge line. 
Dimensions . — The breadth is twelve centimetres ; the diameter from 
the beaks to the ventral margin twenty-seven centimetres ; the length of the 
hinge line nine centimetres ; the thickness near the beaks seven centimetres, 
and three centimetres at a distance of six centimetres from the ventral 
margin. 
