410 AMERICAN TESTUDINATA. Part II. 



ern side of the American continent, and not at all to the west of the Rocky 

 Mountains, or even in their immediate vicinity ; since we cannot fail to see, in 

 this apparently anomalous distribution, another instance of the remarkable similarity, 

 pointed out by the founder of the Physical Geography, between the eastern or west- 

 ern shores of our continents when respectively compared with one another, in their 

 physical features, and in the character of their inhabitants. 



There is another fact of general interest connected with this family, — its exist- 

 ence in Europe, in past geological ages, while no trace of these Turtles can be 

 found there now. The fact is well authenticated : two very distinct species of 

 Chelydroids, from the Miocene beds of Oeningen, near the Lake of Constance, have 

 been described and handsomely illustrated by Th. Bell^ and Herm. von Meyer.^ But 

 what is the meaning of such a phenomenon ? I am inclined to think that the 

 early introduction of this family, in Euroj^e, during the Tertiary period, became an 

 inducement for their reproduction, in" a later age, upon other continents, one 

 of which, at least, bears every characteristic of having been, long before Europe, 

 and for ages past, essentially what it is now, as far as its physical features are 

 concerned. I wovild, therefore, suggest that America has among its Testudinata 

 old-fashioned types, because it is the oldest continent, and not because Chelydra 

 is any more characteristic of the American fauna than of the European. I shall 

 presently call attention again to this point. 



The eggs of the Chelydroidaj, like those of the Trionychidte and Chelonii, are 

 spherical ; but they are liable to occasional variations, those of Chelydra serpen- 

 tina at least, for I have twice obtained ovate eggs from their nests, and once 

 found an ovate one in its ovary (PL 7, fig. 25). Among the spherical ones 

 (fig. 24 and 26) there is also some variation as to size, and to a less extent 

 respecting the hardness of the shell. I have no reason to infer from these 

 facts that the eggs of Testudinata are generally liable to great variations, because 

 the family of the ChelydroidsB stands, as it were, between the lower families with 

 spherical eggs and the higher families with ovate eggs, and we should expect 

 a stronger tendency to unusual combinations in animals holding such a position 

 than in others ; though it must not be forgotten that there is also some dispo- 

 sition to vary among the eggs of the families in which they are oval, and that 

 the highest Testudinata lay spherical eggs like the lowest. This last fact seems 

 to me strongly to vindicate the view which I have already expressed, that the 

 Testudinina are not absolvitely higher than the other natural groups of this type, 

 and cannot, therefore, be considered in the light of a sub-order coequal with the 

 Chelonh proper. (Compare p. 249.) 



^ Proc. Geol. Soc, London, 1831. - Zur Fanna der Vorwelt., 1 vol. fol. 



