. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. 292 HISTORICAL PALEONTOLOGY. after the Middle Eocene period. During that period, the sea prevailed where these chains now rise; for Nummulites and their accompanying Testacea were unquestionably inhabitants of salt ; The Ccelenterates of the Eocene are represented principally by Corals, mostly of types identical with or nearly allied to those now in existence. Perhaps the most characteristic group of these is that of the Turbinolidce, compris
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. 292 HISTORICAL PALEONTOLOGY. after the Middle Eocene period. During that period, the sea prevailed where these chains now rise; for Nummulites and their accompanying Testacea were unquestionably inhabitants of salt ; The Ccelenterates of the Eocene are represented principally by Corals, mostly of types identical with or nearly allied to those now in existence. Perhaps the most characteristic group of these is that of the Turbinolidce, comprising a number of simple " cup-corals," which probably lived in moderately deep water. One of the forms belonging to this family is here figured (fig. 215). Besides true Corals, the Eocene deposits have yielded the remains of the " Sea- pens " {FeimatulidcE) and the branched skeletons of the "Sea-shrubs" {GorgojiidcE). The Echiiiodejins are represented prin- cipally by Sea-urchins, and demand nothing more than mention. It is to be observed, however, that the great group of the Sea- lilies {Crinoids) is now verging on extinc- tion, and is but very feebly represented. Amongst XhtMolh(sca,i\\Q Folyzoa?is and B?'achwpods also require no special men- tion, beyond the fact that the latter are greatly reduced in numbers, and belong principally to the existing genera Te?'€- bratula and RhyncJionella. The Bivalves i^Lamellibraiichs) and the Univalves {Gas- teropods) are exceedingly numerous, and almost all the principal existing genera are now represented; though less than five per cent of the Eocene species are identical with those now living. It is difficult to make any selection from the many Bivalves which are known in deposits of this age; but species of Cardita, Crassatclla, Leda, Cyrena, Madra, Cardium, Fsa?njfiobia,&:c., may be mentioned as very characteristic. The Cardita planicosta here figured (fig. 216) is not only very abundant in the Midd
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