Chap. XL] AFFINITIES OF EXTINCT SPECIES. m 



this ordePj from the continued effects of extinction and 

 divergence of character, has become divided into several 

 sub-families and families, some of which are supposed 

 to have perished at different periods, and some to have 

 endured to the present day. 



By looking at the diagram we can see that if many 

 of the extinct forms supposed to be imbedded in the 

 successive formations, were discovered at several points 

 low down in the series, the three existing families on 

 the uppermost line would be rendered less distinct from 

 each other. If, for instance, the genera a^, a^, a^°, 

 P, m^, m*, m", were disinterred, these three families 

 would be so closely linked together that they probably 

 would have to be united into one great family, in near- 

 ly the same manner as has occurred with ruminants 

 and certain pachyderms. Yet he who objected to con- 

 sider as intermediate the extinct genera, which thus 

 link together the living genera of three families, would 

 be partly justified, for they are intermediate, not direct- 

 ly, but only by a long and circuitous course through 

 many widely, different forms. If many extinct forms 

 were to be discovered above one of the middle hori- 

 zontal lines or geological formations — for instance, 

 above No. VI. — but none from beneath this line, then 

 only two of the families (those on the left hand, a^*, &c., 

 and h^*, &c.) would have to be united into one; and there 

 would remain two families, which would be less distinct 

 from each other than they were before the discovery of 

 the fossils. So again if the three families formed of 

 eight genera (a" to m"), on the uppermost line, be sup- 

 posed to differ from each other by half-a-dozen impor- 

 tant characters, then the families which existed at the 

 period marked VI. would certainly have differed from 



