220 
only of iiTegnlaiiy-distribnted, fine, concentric, rings of growth ; the presence 
of which enabled me to restore and determine the only specimen sent me, 
which was much broken. 
Dimensions. — The length is ten, breadth 11’5, and thickness eight, 
centimetres. 
Delations and Differences. — In size this species resembles IlcBonia 
grandis, J. D. Dana, it differs from it essentially by the sniuosity of its ventral 
margin, and by its much more anterior and more tumid beaks. 
Horizon and Localities. — I have no exact information with regard to 
the horizon of this species, but I believe I am right in considering it 
Carboniferous. Mr. B. Clarke found it in a grey limestone at Coolalamine. 
He Avished me to dedicate it to myself. 
M-EONIA elongata, J. D. Dana. 
Plate XX, Pig. 6. 
31yonia elongata, J. D. Dana, 18t7, Am. Journ. Sci., IV (2), p. 158. 
31ceonia ,, Idem, 1819, Geol. Wilkes’ U.S. Explor. Exped., p. G95, pi. 5, fig. 3. 
This is a large, thick, elongated shell, nearly twice as long as broad, 
and a little compressed and angular posteriorly. According to J. D. Dana 
the right valve is slightly thicker than the other. The beaks are tumid, 
recurved, and placed in the anterior fourth of the valves. An oblique 
depression originating at the beaks reaches to the posterior third of the 
ventral margin, and there causes a well-marked sinuosity, at the same time 
producing a decided inflation Avhich following the same oblique direction, ends 
in the junction of the anal and ventral margins. The posterior side is 
obliquely truncated. The external surface is covered Avith numerous, con- 
centric, unequal, Avell-marked AAU’inkles. The muscular impressions are large 
and transversely striated. 
Dhnenslons. — The length is fourteen, breadth seven, thickness six and 
a half, centimetres. 
Delations and Differences . — Tliis large and beautiful Mceonia cannot 
be confounded A\dth any other species ; I knoAV of none Avith AAdiich it 
could be compared ; it is a kind of transition form between Dleurophorus 
and Ilceonia. 
