XIV 
INTRODUCTION. 
rule is that of Testudo indica , which is found on the Gallapagos, at the Cape of 
Good Hope, and in India. From all the information I have been able to 
obtain, I feel convinced that it is originally and truly indigenous only to the 
former habitat, having been naturalized in the other countries, after being 
casually introduced through the medium of commerce. The writings of 
Lacepede and of other writers of his period, are replete with errors of this 
kind. Thus Testudo grceca is referred to Europe, Asia, Africa and America, 
as its different habitats. It is indeed only within a few years that the geogra¬ 
phical distribution of animals has been considered in the important light which 
it deserves; and the mistakes which arose from the want of giving it its due 
consideration, have consecpiently been, in many instances, corrected. It is how¬ 
ever equally important that we avoid laying down rules of this kind as univer¬ 
sal, without sufficient information. It is certainly an interesting fact, that in 
the case of birds, of insects, and of some other classes, there are very many 
whole groups which, according to our present knowledge, appertain exclu¬ 
sively to the Eastern or the Western World. In the present order, this obtains 
only to a very limited degree. The genus Testudo , it is true, is, generally 
speaking, a form belonging to the Old World; but there are two species, 
nearly allied to each other, T tabulata and T carbonaria , which inhabit the 
Continent of America, besides T indica , found on the Gallapagos. Species of 
the genus Emys are found in each of the four quarters of the globe,—a state¬ 
ment which is generally true of all the fresh-water forms, excepting the genus 
Chelydra , the only recent species of which is exclusively American. I have how¬ 
ever a fine fossil species of this genus (Ch. Murchisonii,') from (Eningen, which 
differs only from Ch. serpentina in some proportions of different parts of the 
skeleton. The genus Hydraspis is principally confined to South America, yet 
H. galeata is a native of the Cape of Good Hope, of India, and of Madagascar, 
and H. longicollis of Australia. The Emydes of the two Hemispheres have 
some remarkable distinguishing characters, by which they may be readily 
discriminated. To these peculiarities I shall have occasion to recur. The 
species of the genus Trionyx are African or Asiatic, with the single exception 
of Tr. ferox, which inhabits the hot regions of America. 
