330 
GEOLOGICAL SUCCESSION^. 
Chap. X. 
wide difference between the pig and the camel. In re¬ 
gard to the Invertebrata, Barrande, and a higher autho¬ 
rity could not be named, asserts that he is every day 
taught that Palaeozoic animals, though belonging to the 
same orders, families, or genera with those living at the 
present day, were not at this early epoch limited in such 
distinct groups as they now are. 
Some writers have objected to any extinct species or 
group of species being considered as intermediate be¬ 
tween living species or groups. If by this term it is 
meant that an extinct form is directly intermediate in 
all its characters between two living forms, the objec¬ 
tion is probably valid. But I apprehend that in a 
perfectly natural classification many fossil species would 
have to stand between living species, and some extinct 
genera between living genera, even between genera be¬ 
longing to distinct families. The most common case, 
especially with respect to very distinct groups, such as 
fish and reptiles, seems to be, that supposing them to be 
distinguished at the present day from each other by a 
dozen characters, the ancient members of the same two 
groups would be distinguished by a somewhat lesser 
number of characters, so that the two groups, though 
formerly quite distinct, at that period made some small 
approach to each other. 
It is a common belief that the more ancient a form 
is, by so much the more it tends to connect by some of 
its characters groups now widely separated from each 
other. This remark no doubt must be restricted to 
those groups which have undergone much change in the 
course of geological ages; and it would be difficult to 
prove the truth of the proposition, for every now and 
then even a living animal, as the Lepidosiren, is dis¬ 
covered having affinities directed towards very distinct 
groups. Yet if we compare the older Eeptiles and 
