SNAKES. 37 



** Labial shield occupying the front half of the lip ; eyes over the 

 fifth or sixth shield ; hinder part of the face covered ivith small 

 scales; ventral scales generally tivo-ro7ved, forming a keeled 

 ridge, some united in pairs into six-sided shields. 



9. Hydeus. 



c. Body covered with smooth, polished, imbricate scales : head 

 as large as the body : ventral shields rather large, trans- 

 verse, smooth, folded together and keeled. 



10. ToMOGASTER. Head with regular sMclds ; superciliaiy shields 



simple ; ventral shields entire. 



11. SxEPHANOHYDRA. Head shields numerous ; superciliary shields 



3 or 4 ; ventral shields nicked behind. 



B. Head covered with scales, like the body : nostrils surrounded by a 

 small, continuous ring : eyes surrounded by a series of small 

 scales ; labial shields small, with a larger series above them : 

 pupil round : ventral shields very small, scale-like, separated on 

 each side of a keeled ridge. Elvers. Acrochordina. 



12. Chersydeus. Tail compressed, sword-shaped, prehensile: 



body fusifonn, covered with small rhombic scales, with a cen- 

 tral tubercular keel. 



13. AcROCHORDUS. Tail conical, tapering, moderate: body fusi- 



form, covered with tricuspid scales. 



II. Tail conical, tapering. Belly rounded beneath, luith more or less 

 broad band-like shields. Rivers or ponds. 



A. Head shielded : tail scaly beneath : abdominal shields flat, small, 



six-sided, with a keel on each side, as if formed of two united 

 scales : nostrils in a ring of small scales : scales keeled. Erpe- 

 tonina. 



14. Erpeton. 



B. Head shielded : tail with two series of shields beneath : nostrils 



between tivo shields : abdominal shields broad, keeled on each 

 side : scales smooth. Bitiana. 



15. BiTiA. Head small. 



E 



