XXIII] CHELONIA 597 



wall of the cloaca. The groove leads to the openings of the male 

 ducts, the vasa deferentia. 



The members of the order Chelonia have very various habits and 

 modes of life. Some are vegetable feeders, others purely animal. 

 None are found in Great Britain, but the representatives of six 

 groups are found in temperate North America. These are 



(1) The TESTUDINIDAE or Land Tortoises. 



(2) The EMYDIDAE or "Pond Turtles. 



(3) The CINOSTERNIDAE or Box Turtles. 



(4) The CHELYDRIDAE or Snapping Turtles 



(5) The TRIONYCHIDAE or Mud Turtles. 



(6) The CHELONIDAE or Marine Turtles. 



The TESTUDINIDAE have a very arched carapace and short club- 

 like limbs in which the toes are tightly bound together by skin. Only 

 a few species, Testudo polyphemus, the burrowing Gopher, and Cistudo 

 Carolina, the Box Tortoise, are known in temperate North America. 



The EMYDIDAE are represented by many species. In this family 

 the carapace has a wide horizontal margin and the toes are con- 

 nected by a web. Most of the species are aquatic, a few however 

 are almost as terrestrial as the TESTUDINIDAE. Chrysemys picta, 

 the Painted Pond Turtle, ranges north into the St Lawrence. 



The CINOSTERNIDAE have a long and narrow carapace with the 

 margins produced downwards ; it is highest behind. The front part, 

 and sometimes the hind part, of the plastron moves like a hinge on 

 the rest and close in the head and tail, whence the name Box 

 Turtle. Sole genus Cinosternum. C. pennsylvanicum is the most 

 northerly species. 



The CHELYDRIDAE are the so-called Alligator- or Snapping- 

 Turtles. The head, neck and tail are all large and cannot be 

 completely protected between the carapace and plastron. The 

 carapace is highest in front. The jaws are hooked and powerful 

 and the animals are very vicious. Chelydra serpentina, the 

 "Snapper," is one of the commonest of American turtles. It is 

 found everywhere from Canada to the tropics. 



The TRIONYCHIDAE or Mud Turtles have no horny scales ; both 

 carapace and plastron are covered with leathery skin. There is a 

 soft pig-like snout ; only the three centre toes have claws. They 

 seek their food by burrowing in the bottom of ponds. 



The CHELONIDAE are distinguished by their peculiar skull and 

 the absence of many or all of the nails. Their extremities have 

 become flattened and form very efficient paddles. 



