CHAPTEE IV. 

 CHELONIANS, OR SHIELDED REPTILES. 



[" THE body," as described by Dr. Gray, " is covered with square 

 imbedded plates, generally forming a dorsal and ventral shield 

 united by their margins, leaving only the head, neck, limbs, and 

 tail free, and (in some species, as the Box- Tortoises, Cinasternon, 

 shut up by movable closely-fitting doors) only covered with a scaly 

 skin ; the upper shield formed of the ribs united together and 

 adherent to the dorsal vertebrae by a toothed suture, and surrounded 

 by a series of bones forming the edge of the shields ; the lower 

 shield, or sternum, formed of four pairs and a central anterior 

 bone ; the jaws toothless, covered with a horny bill, rarely hid by 

 fleshy lips ; eyelids distinct ; drum of the ear visible ; legs short 

 and thick ; tail conical." " The natural dwelling chamber of the 

 Chelonia consists chiefly," says Professor Owen, "and in the 

 marine species (Ckelone) and Mud Turtles (Trionyx) solely, of the 

 floor and the roof; side- walls of variable extent are added to the 

 fresh- water species (Emydians) and Land Tortoises (Testudinians). 

 The whole consists of ' osseous plates/ with superincumbent horny 

 plates, or ' scutes/ except in the Soft or Mud Turtles (Trionyx 

 and Sphargis), in both of which these are wanting." (" Circle of 

 the Sciences.") 



These animals, to which a portable stronghold is thus given 

 in compensation for inferior powers of locomotion and defence, 

 are recognisable at a glance from the singular armour with 

 which Nature has provided them. A double shield envelopes all 

 parts of their bodies, only permitting the head, neck, legs, and 



