80 



REPTILIA. 



Genus IV. Trionyx. Soft Tortoise. 



No scales ; merely a soft skin to envelope their carapax and 

 plastron. 



ORDER II. SAURIA. 



Heart like that of the ChelonicB ; ribs movable, partially 

 connected with a sternum, and serving for respiration ; lungs 

 more or less extended towards the posterior extremity of the 

 body ; skin covered with scales or hard granulations called 

 shagreen ; mouth always armed with teeth ; toes generally 

 provided with nails ; tail more or less long ; most usually four 

 legs, sometimes only two ; eggs enveloped in a hard and cal- 

 careous shell. Six families. 



FAMILY I. CROCODILIDA. 



Animals of large size ; tail flattened laterally, which ren- 

 ders them aquatic ; four limbs; five toes before, four behind, 

 more or less palmated ; only the three internal ones armed 

 with claws; a single row of pointed teeth in each jaw ; tongue 

 fleshy and flat, and adhering close at its edges ; the back 

 and tail covered with large square scales, relieved by a ridge 

 along their middle ; those of the abdomen fine and smooth ; 

 a crest with strong indentures on the tail, double at the base; 

 ventricle of the heart divided into two chambers, made dis- 

 tinct by a complete partition ; instinct carnivorous ; habita- 

 tion in fresh waters. Three genera. 



Genus I. Crocodilus, Briss. Crocodile proper. 



The fourth tooth of the under jaw passing into a notch of 

 the upper jaw ; teeth of unequal size ; muzzle moderate and 

 depressed horizontally ; toes of posterior limbs entirely pal- 

 mated. [Both Continents.] 



Genus II. Gavial, Cuv. 



The fourth tooth of the under jaw passing into a notch of 

 the upper ; teeth equal ; muzzle long, slim and cylindrical ; 

 toes of the posterior limbs entirely palmated, [The old con- 

 tinent only.] 



