TRIONYX EMYS. 197 



The genera Trionyx and Emys, present their fossil 

 species in the Wealden fresh-water formations of the Se- 

 condary series ; and still more abundantly in the Tertiary 

 lacustrine deposites ; all these appear to have lived and 

 died under circumstances analogous to those which attend 

 their cognate species in the lakes and rivers of the present 

 tropics. They have also been found in marine deposites, 

 where their admixture with the remains of Crocodilean 

 animals shows that they were probably drifted, together 

 with them, into the sea, from land, at no great distance.* 



In the close approximation of the generic characters of 

 these fossil Testudinata, of various and ancient geological 

 epochs, to those of the present day, we have a striking ex- 

 ample of the unity of design which has pervaded the con- 

 struction of animals, from the most distant periods in which 

 these forms of organized beings were also called into ex- 

 istence. As the paddle of the Turtle has at all times been 

 adapted to move in the waves of the sea, so have the feet 

 of the Trionyx and Emys ever been constructed for a more 

 quiescent life in fresh-water, whilst those of the Tortoise 

 have been no less uniformly fitted to creep and burrow upon 

 land. 



5, Pt. 2, Tab. 14, /, 4, of the Oss. Foss. ofCavier. M. Agassiz has favoured 

 iiie with the following details respecting important parts which are imper- 

 fectly represented in the drawing from which Cuvicr's engraving was taken. 

 " The ribs show evidently that it is nearly connected with the genera Che- 

 Ionia and Sphargis, bat referable to no known species ; the fingers of the 

 left fore paddle are five in number; the two exterior are the shortest, and have 

 each three articulations; and the ihree internal fingers, of which the middle 

 one is the longest, have each four articulations, as in the existing genera, 

 Chclonia and Sphargis." 



* Thus two large extinct species of EmyK occur, together with marine 

 shells, in the jura limestone at Soleure. The Emys also and Crocodiles, are 

 found in the marine deposites of the London clay at Shoppy and Harwich; 

 and the former is associated with marine exuvix at Brussels. Very per, 

 fret impressions of small horny scales of Testudinata, occur in the Oolite 

 slate of Stonesfield, near O.vford. 



17* 



