302 



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 water. " 



The Ccelenterates of the Eocene are represented principally 



by . Co r-als, mostly of types identical with or nearly allied to 



those now in existence. Perhaps the most characteristic group 



of these is that of the Turbinoiida, 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 " (Pennatulida} and the branched 

 'skeletons of the " Sea-shrubs " (Gorgonidcz}. 

 ' The Echinoderms 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 the Mollusca, the Polyzoans 



and Brachiopods also require no special men- 



tion, beyond the fact that the latter are 



greatly reduced in numbers, and belong 



principally to the existing genera Tere- 



bratula and Rhynchonella. The Bivalves 



(LamellibrancJis} 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 thos-e now living. It is difficult to 



make any select-ion from the many Bivalves 

 which are- known in deposits of this age ; 



but species of -Cardtia, Crassatella, Leda, 

 '.Cyrena,- Mactra, Cardium, Psammobia, &c., 



may be mentioned as verv characteristic 

 The Cardita planicosta here figured (fig! 



216)- is not only very abundant in the 



Middle Eocene, but is very widely distrib- 



uted, ranging from Europe to the Pacific coast of North 



America. The Univalves of the Eocene are extremely nu- 



merous, and generally beautifully preserved. The majority 



Eocene - 



