Fig. 7. The interior of the upper part or vertex of a large Echinus, from the tertiary strata of Malta. The greater portion of the shell is broken away, but a small fragment showing the outer surface remains on the upper left hand of the specimen. The five large petalous ambulacra are beautifully seen. Perfect examples of this echinite (_Echinanthus Clypeaster altus_, of Parkinson), are not uncommon. Fig. 19. A spine of _Cidaris sceptrifera_, from the chalk of Kent. Fig. 20. An elegant Turban Echinite, (_Hemicidaris crenularis_, of Lamarck,) common in the Coral Rag of Wiltshire. Groups of this beautiful echinoderm, with numerous spines attached, are found at Caen. I have seen on one slab of limestone, upwards of twenty individuals with the spines radiating round the shell, as if the animals were alive on a mud bank in shallow water. Fig. 21. A fragment of the shell with two spines (_Cidaris claviger_), attached to a flint; from Kent. [Illustration: Plate LVII.] PLATE LVII. Fossil Shells. Figs. 1, & 3. Upper and under view of a discoidal spiral univalve shell (_Euomphalus pentangulatus_, of Sowerby), from the mountain limestone of Derbyshire. The extinct genus Euomphalus, a name suggestive of the deeply excavated disk, comprises many species which occur in the Silurian, Devonian, and Carboniferous formations. The shell has chambers, or rather obsolete cavities sealed up by a shelly partition, in the abandoned part of the spire.[52] [Footnote 52: Medals of Creation, pp. 425-427.] Fig. 2. An elegant univalve shell, completely silicified or transmuted into flint (_Natica canrena_, of Parkinson, _Natica Gentii_, of Sowerby), from the upper greensand of Blackdown. Figs. 4, & 6. Two views of the same specimen; a univalve (_Nerita conoidea_, of Lamarck), in which the apex or upper part is destroyed, and the interior of the shell is filled with yellowish brown chalcedony; in fig. 4, a cast of the spire is seen, and in fig. 6, the mouth of the shell, with the chalcedony partially filling up the interior. From tertiary strata near Paris. Fig. 5. A beautiful fossil univalve shell, from the "Red Crag" of Suffolk, known to collectors as the "Essex reversed whelk," from the spire being coiled in the opposite direction to the common mode; the mouth is consequently situated to the left of the observer; the same species occurs with the spire in the usual direction. This shell is the _Murex_ (_Fusus_) _contrarius_, of Parkinson. Figs. 7, & 8. Under and upper view of another species of Euomphalus (_E. rugosus_, of Sowerby), from the Wenlock limestone, Dudley.