209 
Genus — OLAE-KIA, L. G. de Konincle} 
In this genus, the shell is elongated, equivalved, and gaping at its anal 
extremity; its ligament (?) is external; its hinge shows a thick callosity, 
and is composed of a single tooth, projecting a little over each valve, and 
placed directly under the beak. The external surface is perfectly smooth. 
The impressions of the adductor muscles and of the foot are separate ; the 
first are large, oval, and not strongly marked, while the other is small and 
decidedly well-marked. The pallial impression is nearly simj^le, not very 
apparent, and only very sinuous posteriorly. The shell is somewhat thick, 
and its external surface is ornamented with concentric striae of growth. 
Note. — I find myself obliged to create this new genus for a shell 
that seems to me identical with Mceonia myiformis, J. Dana, which does not 
belong to the genus in which the American Palaeontologist has placed it. 
The true Mceonia are carinated, have a simple pallial impression, and two 
hinge teeth. The genus I have created occupies an intermediate position 
between Panopcea and Glycimeris ; it resembles the first by its single tooth, 
and the second by the strong callosity of its hinge ; it differs from both by 
its shell gaping on one side only. So far this genus is represented by the 
single species that I am now about to describe. 
Clarkia myiformis, J. B. Bana. 
PI. XVIII, Fig. 1. 
By ramus myiformis, J. D. Daua, 1817, Am. Jouni. Sci. IV, p. 157. 
Mceonia ,, Idem, 1849, Greol. Wilkes’ U.S. Explor. Exped., p. 697, pi. 6, fig. 4. 
This is an elongated, elliptical shell, witli very small, slightly recurved 
beaks, very close together, and placed at the anterior third of the shell. Its 
internal surface is perfectly smooth. A slight callosity originating at the 
beak extends to the middle of the breadth of each valve. The valves are 
moderately deep, and rather depressed towards their anterior side, which is 
a little broader than the posterior side. I have seen only a small part of 
the external surface of the valves ; it is ornamented with numerous, fine, 
concentric lines of growth. The test is rather solid, from one to two mille- 
metres thick. 
^ I dedicate this genus to the Rev. W. B. Clarke, to whom I am indebted for the collection of fossils 
furnishing the subject of this work. 
