26 REPTILE GALLERY. 



Turtles having their limbs transformed into regular paddles, re- 

 sembling those of Cetaceans. The tail is constantly present, but 

 frequently extremely short; in a few forms only it attains to a con- 

 siderable length. Chelonians are oviparous, and the eggs are 

 generally covered with a hard shell. 



The Chelonians form only a small part of the Class Reptilia, the 

 number of species amounting to about 300. If they occupy in 

 this Gallery almost half of the wall-cases, it is because they are 

 more suited than the other Reptiles for being preserved and exhi- 

 bited in a di'ied state. 



Chelonians are divided into the following Suborders ; — 



1 . SphargidcB, or Leather-Turtles. 



2. Cheloniida, or Sea-Turtles. 



3. Trionychida, or Freshwater Turtles. 



4. EmydidcB and Chelydidce, or Freshwater Tortoises. 



5. Testudinidce, or Land Tortoises. 



In the first three several important characters remind us of 

 other orders of Reptiles, especially Crocodilians, whilst the two 

 last are farthest removed from the ordinary Reptilian type. 



1. The Sp/iargidcB are a geologically ancient type, in which the 

 formation of a protecting bony carapace has made but little 

 advance. The skin, which in a fresh state is flexible, like thick 

 leather, contains bony deposits arranged like mosaic; but this 

 dermal shield is not united to the vertebrse and ribs, which remain 

 free, and are not particularly dilated, as may be seen in the large 

 skeleton (G) exhibited opposite to Case 29. In this arrangement 

 the dermal shield and skeleton are in the same relation to each other 

 as in the Crocodiles. The structure of the limbs is the same as in 

 the marine Turtles, with which the Leather-Turtle agrees in its 

 mode of life; the bones of the paddles, however, are still more 

 simple, merely rods, and claws are entirely absent. Only one 

 species exists ni our time [Sphai'yis coriaceus), which seems to 

 become gradually rarer, although it is found occasionally through- 

 out all the seas of the tropical and temperate regions, specimens 

 having strayed now and then to the British coast. This Turtle is, 

 perhaps, the largest living Chelonian, exceeding a length of 6 feet, 

 and is said to be herbivorous. 



