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shell. The beaks are nearly terminal. The anterior ear is very small, the 
posterior rather long and produced liy an oblique keel-shaped gibbosity, 
extending from the beak to the jiosterior extremity of the ventral margin, 
which is slightly arched. The posterior margin is obliquely truncated and 
rather sinuous. The surface is covered with irregular, concentric rings of 
growth. This small species has a relatively large hinge area nearly a milli- 
metre broad. 
B vmensions. — The length is twenty-seven, the breadth ten to eleven, 
and the thickness of the right valve five to six millimetres. 
Relations and Bifferences. — It is rather like A. lunulata, Phillips, but 
differs from it by being narrower and much less oblique. Perhaps it is identieal 
with Cypricardia imbricata, Dana, which seems to me to he an Avicula, but 
I have had no opportunity of comparing them in nature. 
Horizon and Localities . — A single internal cast of this species was 
found in a yellowish sandstone at Muree. 
Avicula Haudyi, L. G. de Koninck. 
PL XVr, Pig. 10. 
This shell is small, elongated, suhrhomhoidal, and crossed obliquely by 
a keel-shaped gibbosity, which starts at the beak and extends to the posterior 
extremity of the ventral margin, there dividing into two nearly equal parts. 
The beak is terminal, small, and recurved. Immediately below it is a very 
small ear, produced by a decided sinuosity corresponding to the byssal notch. 
The ventral margin is slight arched, and the anal margin obliquely truncated. 
The surface is ornamented with small concentric lines of growth, scarcely 
perceptible to the naked eye. 
Bimensions. — The length is about twenty, the breadth eleven, and the 
thickness of the left valve three millimetres. 
Relations and Bifferences. — This species differs from A. mconspiciia, 
Phillips, by the anterior position of its beaks, and by the sinuosity giving 
rise to the anterior ear. 
Horizon and Localities. — The only specimen sent me came from 
Burragood. 
2 K 
