REPTILIA. 289 



II. SERPENTID^. No third eyelid: abdomen 

 covered with broad transverse plates : jaws 

 dilatable : no vestiges of bones of the sternum 

 and shoulder. 



5. NATRIX. Subcaudal plates arranged in pairs : 

 four nearly equal rows of imperforate teeth above, and 

 two below : no poison-fangs. 



6. VIPERA Subcaudal plates arranged in pairs: 



maxillaries armed with poison-fangs, but without ordinary 

 teeth. 



T 



