410 
EOCENE FOSSILS. 
of known species has in the interval hecome nearly double in number. 
On the Continent, however, this great break in the succession of 
strata is not nearly so marked, and in North America the series 
connecting the two formations is fiiirly represented by the Laramie 
formation. 
This period in this country embraces three groups of strata, the 
Eocene, the Oligocene, and the Pliocene formations, the predominating 
development of the Gastropoda being the most remarkable feature of 
the period, but also showing a much more decided approximation to 
the present inhabitants of our country generally, the proportion of 
living to extinct species increasing from perhaps 5% in the Eocene to 
7.")% or more in the later deposits. 
Few remains of our present species are found earlier than the Eocene 
beds of the d'ertiary period, and in this country many strata, which 
would probably have yielded large numbers of fossils, have been swept 
away by the extensive denudations extending over vast ages of time, 
so that not even fragmentary relics are now available for study. 
The Eocene (h'js-, dawn; Kiunk, recent) is the oldest of the tertiary 
group, its deposits chielly occuj)ying two great depressions in the 
chalk, known as tlie London and Hampshire basins, and being con- 
sidered to sIkjw the origin or dawn of the lU’csent fauna of the earth, 
as its beds contain remains of genera which although now extermi- 
nated in this country, still exist in closely-related forms in the more 
remote regions of the globe, showing that a different geographical 
distribution of organisms from the present existed in former times. 
Many genera of mollusca whicli were in Eocene times inhabitants of 
this country are now restricted to other and distant climes, as A mphi- 
(Iromns which is nf)W found chiefly in the Indo-Mala 5 "an region, 
Camptocenoi now ccmtined to India, etc. 
The following are the known s})ecies from this formation : — 
imi.IMUI.IO.E. 
Amphidroiinia ri/li/riisis (Hoissy), 
fouiixfi'iiitiis (Sow. ). 
I’UIMD.E. 
Megaspim ri/lindricK Newt. & Harris. 
LIMN.Ein.E. 
Liinnari ri/liiidrir(( Newton ik' Harris, 
Pitluircllii rirliiiiiiii Edwards, 
P/tiuftrlds ciioiiijdi(di(ti •). Sow., 
licin'istunia .1. Sow.. 
invcrtna Newton ik Harris, 
Id riijdt ns Desli., 
Ci( iiipfarcrds /irisfii in ( iod win-.\nsten, 
— V. ohtnsa (iodwin-Austen, 
AURICULID.E. 
Pcdipcs gldhcr Edward.s. 
MELANtlO.E. 
Mddnin hegscdna Pliilippi, 
Mcldnopsis dncdldrioidrs Desliayes, 
hurcinoiden Eer., 
huirinidnm Desliayes, 
cdrindtu .1. de ('. Sow., 
inin-ostiinid Edwards MS., 
2 iseiulo-siiljuldtd Newton, 
solid/ is Desli., 
Meld ndtrid ignotn Edwards MS., 
inipiindtd ( Defrance), 
vidciinica (Sehlotli). 
