In that rich storehouse of fossils, the Cornbrash, there occur, as all geologists who have been in the habit of collecting from it are aware, several species of the genus Ostrea, two of which are large and conspicuous shells. One of these is the everywhere abundant and very characteristic plicated form known, as O. Marshii, Sow. (O. flabelliformis, Lamk.?); the other, which is far less common, but by no means rare, is flat and smooth, and sometimes considerably elongated in form. This latter species does not appear to have received a name in this country, but it may not improbably be identical with the O. exarata of Goldfuss (Petrifacta Germaniæ, Theil ii. z. 5, tab. 72, fig. 9), a shell first obtained from the Unteroolith of Gräfinberg.