38 EEPTILES. 



C. Head shielded : scales striated, and keeled or smooth : tail co- 

 nical, tapering, with tiuo series of shields beneath : nostrils in 

 centre of a large nasal shield, with a groove to the outer side : 

 ventral shields rounded (or rarely slightly keeled on the sides) ; 

 frontal shields 3, rarely 2 or 4, all small. Cerberina. 



a. Crotvn scaly ; occipital rudimentary ; frontals 4 ; anterior 

 pair very small. 



16. Cerberus. Scales keeled, striated ; hinder labial shield low. 



b. Crown shielded ; occipital moderate. 



■* Head distinct, depressed ; frontals 4 ; anterior pair small ; rostral 



rounded. 



17. Ferania. Scales smooth; seventh upper labial low, with a 

 large shield over it. 



** Head distinct, depressed ; frontals 3 ; anterior transverse ; rostral 



rounded. 



f Fourth and fifth hinder labial shields small or divided. 



18. HoMALOPsis. Scales keeled. 



19. Phytolopsis. Scales smooth. 



ff Hinder labial large, like others ; scales keeled ; rostral rounded. 



20. Uranops. Scales truncated, strongly keeled, striated; eye 



over fourth shield. 



21. Tachynectes. Scales truncated, strongly keeled. 



22. Tropidophis. Scales ovate, keeled, striated ; eye over fourth 



and fifth shield. 



23. Myron. Scales ovate, slightly keeled, smooth. 



24. Helicops. Scales ovate, polished ; of back and tail keeled. 



