Chap. XL Affinities of Extinct Species. 301 



compares certain stages in England with those in France, although 

 he finds in both a curious accordance in the numbers of the species 

 belonging to the same genera, yet the species themselves differ in 

 a manner very difficult to account for considering the proximity 

 of the two areas, — unless, indeed, it be assumed that an isthmus 

 separated two seas inhabited by distinct, but contemporaneous, 

 faunas. Lyell has made similar observations on some of the later 

 tertiary formations. Barrande, also, shows that there is a striking 

 general parellelism in the successive Silurian deposits of Bohemia 

 and Scandinavia ; nevertheless he finds a surprising amount of 

 difference in the species. If the several formations in these regions 

 have not been deposited during the same exact periods, — a forma- 

 tion in one region often corresponding with a blank interval in the 

 other, — and if in both regions the species have gone on slowly 

 changing during the accumulation of the several formations and 

 during the long intervals of time between them ; in this case the 

 several formations in the two regions could be arranged in the same 

 order, in accordance with the general succession of the forms of life, 

 and the order would falsely appear to be strictly parallel ; never- 

 theless the species would not be all the same in the apparently 

 corresponding stages in the two regions. 



On the Affinities of Extinct Species to each other, and to Living 



Forms. 



Let us now look to the mutual affinities of extinct and living 

 species. All fall into a few grand classes ; and this fact is at once 

 explained on the principle of descent. The more ancient any form 

 is, the more, as a general rule, it differs from living forms. But, 

 as Buckland long ago remarked, extinct species can all be classed 

 either in still existing groups, or between them. That the extinct 

 forms of life help to fill up the intervals between existing genera, 

 families, and orders, is certainly true ; but as this statement has 

 often been ignored or even denied, it may be well to make some 

 remarks on this subject, and to give some instances. If we confine 

 our attention either to the living or to the extinct species of the 

 same class, the series is far less perfect than if we combine both into 

 one general system. In the writings of Professor Owen we continually 

 meet with the expression of generalised forms, as applied to extinct 

 animals ; and in the writings of Agassiz, of prophetic or synthetic 

 types ; and these terms imply that such forms are in fact inter- 

 mediate or connecting links. Another distinguished palaeontologist, 

 M. Gaudry, has shown in the most striking manner that many of 

 the fossil mammals discovered by him in Attica serve to break 



