292 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 Cwlenterates 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 Zurbinolide, 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” (Pennatulide) and the branched 
skeletons of the “‘Sea-shrubs” ( Govgonide). 
The £chinoderms are represented prin- 
cipally by Sea-urchins, and demand nothing 
more than mention. Itis 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 A7o//usca, the Polyzoans and 
LBrachiopods also require no special men- 
tion, beyond the fact that the latter are 
greatly reduced in numbers, and belong 
principally to the existing genera TZere- 
bratula and Rhynchonella. ‘The Bivalves 
(Lamellibranchs) 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 sfecies 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., 
Fig. 215.—Turbinolia may be mentioned as very characteristic. 
Sia) Janta oe The Cardita planicosta here figured (fig. 
Eocene. 216) is not only very abundant in the 
Middle Eocene, but is very widely distri- 
buted, ranging from Europe to the Pacific coast of North 
America. The Uvivalves of the Eocene are extremely nu- 
merous, and generally beautifully preserved. The majority 
of them belong to that great section of the Gasterofods in 
which the mouth of the shell is notched or produced into 
