CHELOMA. '2-~> 



Sub-order Proccelia = Crocodilia, $.fi-. 



With proccelous vertebrae and long compressed swimming tall, tin- 

 dorsal side of which bears a double cutaneous crest, which becomes 

 single at the posterior end. The anterior feet with five free digits ; 

 the posterior with four digits, which are more or less united by 

 webs. Live in the mouths and lagoons of great rivers in the warmer 

 climates of the Old and New Worlds, and seek their prey by night. 

 The hard-shelled eggs are laid in the sand and in holes on the banks. 



Fain. Crocodilidae. The so-called canine teeth (fourth tooth of the lower 

 j;i\v) fit into a notch of the margin of the upper ja\v. Hind feet with com- 

 plete swimming membram-. (.'rncot/ih/x n/ii/i/rix (.,'uv., Xile. ('. rhoiiibifrr 

 ( 'uv,. i 'uba. 



Kam. Alligatoridae. The snout is broad and without notch for the so-called 

 canines of the mandible. Swimming membranes only partially developed or 

 rudimentary. [Found only in America.] ARiijutor lucius CUT. ; Caiman 

 (J/ic/ii'/') xdt >-oj>x Schn. 



Fam. Gavialidae. Rhamj}1ixt<n<t f/n/it/rf in/in Geoffr.. East Indies; Khynclt- 

 ii.ini-fiitx Xi-hli'i/rlli (iray, Australia. 



Sub-class 3.- CHELONIA.* 



Reptilia of short, stout form of body, with an upper and lower 

 osseous shield which covers the dorsal and ventral surfaces. There are 

 four feet, and the jaws are without teeth. 



No other group of Reptiles is so clearly defined and characterised 

 to the same extent by peculiarities of form and organisation as is 

 that of the Chelonia. The investment of the body by an upper, 

 more or less arched and usually osseous dorsal shield (carapace), and 

 by a lower ventral shield (plastron), joined to the former by lateral 

 arches, forms a character as distinctive of the Chelonia as is the 

 posses>ion of wings and feathers of the class Aves. 



The shield-like, dermal, armour (fig. 646) beneath which the head 

 extremities and tail can often be retracted, owes its origin partly to 

 osseous parts of the vertebral column and partly to the accessory der- 

 mal bones, which are intimately connected with the former. The 

 flat plastron contains nine more or less developed osseous pieces, an 

 anterior unpaired interclavicular, and four pairs of lateral pieces (the 

 anterior being distinguished as clavicularia) between which there 



* H. Rathke, " Ueber die Entwickelung der Sdiildkrb'ten," Braunschweig. 

 184s. 



Gray, " Catalogue of the Shield Reptiles in the Collection of the British 

 MiiM'iim. I'art L. London IS.")."). Suppl., ISTu. Append.. 1S72. 



L. Agassiz, " Embryology of the Turtle." Natural History of the United 

 States, Vol. 111., part III., 1857. 



VOL. II. 15 



