Chap. I. GEOGRAPHICAL DISTRIBUTION. 301 



SECTION XVI. 



GEOGUAl'IlICAL DISTKIULTIUN OF THE TESTUDINATA. 



The distrihution of the Testudinata upon the surface of our glol)e presents 

 some very interesthig features, whicli deserve the more to ai'rest our attention, as 

 they bear directly upon the very principles -which regulate the geographical dis- 

 trilnition of the animals in general. In the first place, "we find that, taken as 

 a whole, the range of the Testudinata is less extensive than that of the other 

 orders of Reptiles. This agrees with the general fact, that the higher representa- 

 tives of any comprchen-sive group are everywhere more limited in their distribution 

 than the lower types of the same group ; and as we have seen that the Testu- 

 dinata are the highest Reptiles, we should expect to find them, as is really the 

 case, occupying a more limited area of the surface of the globe than either the 

 Saurians or the Ophidians. This is equally true of their horizontal and of their 

 vertical range. A few Saurians, and some Oj^hidians, esj^eciallj^ of the family of 

 Vipers, extend much fiirther north, and much higher up, along the slopes of the 

 mountains, than any Chelonians. In the second place, it is known that the sea Tur- 

 tles, the Chelonii proper, which constitute the lowest .sub-order of the Testudinata, 

 have a much wider range than the laud and fresh-water Turtles, the Amydfe. This 

 fact is important in two different points of view : first, as corroborating the asser- 

 tion, already made above, that the lower representatives of any comprehensive group 

 have a wider distribution than its higher types ; and secondly, as showing that the 

 mediums in which the lower types dwell are frequently different from those Avhich 

 suit the higher ones. It is a fact, that though the Testudinata, as a whole, have 

 a more limited geographical range than the other orders of Reptiles, the sea Turtles, 

 which are unquestionably the lowest Testudinata, are hy far more widely diff'used 

 upon the surface of the earth than either the land or fresh-water Turtles. They 

 are common to all ocean.s, being found in the North and South Atlantic as well 

 as in its warmest waters; in the Mediterranean, in the Indian Ocean, and over 

 the whole range of the Pacific. Moreover, marine Turtles have been observed in 

 nortlicrn latitudes, far beyond the range of other Turtles; they are, indeed, tlic duIv 

 ones seen, and that but occa.sionalh', along the northern shores of Europe and of 

 Eastern Asia. It is not less characteristic, that these Chelonii, which are the lowest 

 of the Testudinata, are at the same time all marine, while the Amyda*, which con- 

 stitute a higher sub-order, never live in the ocean, but only upon land, either in 

 fresh water or upon dry laud. 



