136 ECONOMIC ZOOLOGY 



and movable eyelids are present. These are the familiar and easily 

 recognized turtles, terrapins and tortoises. 



2. The Squamata. The characteristics of this order, as a whole, 

 are largely osteological so that we shall consider at once the two sub- 

 orders of living Squamata, which are sometimes considered as distinct 

 orders; they are the Lacertilia and the Ophidia. The former are usually 

 provided with legs for walking; nearly always with eyelids and tympanic 

 membranes; the rami of the mandibles are closely united at the sym- 

 physis and the mouth can open only moderately widely; a sternum is 

 present; they are represented by the various lizards, such as Geckos 

 Iguanas, Chameleons, etc. The latter sub-order, the Ophidia, are the 

 snakes they are much elongated forms without appendages, movable 

 eyelids, tympanum and sternum; the rami of the mandibles are con- 

 nected by elastic fibres, and the mouth can be opened to an extraor- 

 dinary width. 



3. The Crocodilia. The body is here more or less covered with 

 bony scales; a sternum is present and also a set of abdominal ribs: 

 the Cloaca is longitudinal in position and sheaths a medium penis; 

 the legs are adapted for walking and the tail is usually compressed for 

 swimming; the teeth are numerous and held in sockets; the ventricle 

 of the heart, in living species, is completely divided. This order in- 

 cludes as living representatives the familiar crocodiles and alligators 

 and also the gavials and caimans, some of which are the giants of the 

 present reptilian world. 



4. Rhynchocephalia. This order is represented by a single living 

 genus Hatteria or Sphenodon; a lizard-like reptile found in New 

 Zealand. Since its only economic importance is as a specimen no 

 further description will be given here. 



Chelonia or Testudinata. The Chelonia are, by some, divided into 

 three groups, the turtles, the terrapins, and the tortoises, this division 

 being based chiefly upon the habitat of the species, whether terrestrial, 

 aquatic or amphibious. As these names are employed differently by 

 different authors and in different sections of the world, no attempt will 

 be made here to distinguish between them, and the word turtle will be 

 generally used for any member of the order. 



It is as food for man that the chelonia are chiefly important, though 

 there are other economic aspects of the group that will be briefly 

 discussed. 



