Everyone who has collected the fossils of the Upper Chalk will have noticed how the Echinoderms and Belemnites are overgrown by small oyster-like shells with a striated disk, commonly passed by as the fry of Ostrea vesiculosa. There is a beautiful example of Micraster cor-anguinum in the Museum of the Geological Society (given by Mr. Bayfield, of Norwich, to the late Daniel Sharpe), on which a dozen of these little shells, each about half an inch across, have left their lower valves; and above twenty are congregated on a fragment of Ananchytes (occupying a space of about three square inches) in the British Museum.