302 



HISTORICAL PALAEONTOLOGY. 



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 Ccelcnterates 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 Turbinolidcc, 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 " (Gorgonida}. 



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 

 (Lamellibranchs) and the Univalves (Gas- 

 ieropods) 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, Crassatella, Leda, 

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

 may be mentioned as very 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 



Fig. 2l5.Turbinolia 

 aulcata. viewed from one 

 side, and from above. 

 Eocene. 



