BOIDJB. 73 



Lower labials with pits; nostril supero-lateral, in a semidivided 

 nasal 3. Liasis, p. 76. - 



2. Tail prehensile ; rostral and anterior upper labials deeply 

 pitted 4. Python, p. 80. 



B. Prsemaxillary bone toothless. 



Palate toothed; labials pitted; tail prehensile, with two rows of 

 subcaudals 5. Chondropython, p. 90. 



Palate toothed; no labial pits ; taU. not or but very slightly 

 prehensile, with the subcaudals mostly single. 



6. Aspidites, p. 91. 



Palate toothless; no labial pits; no mental groove; tail not pre- 

 hensile ; subcaudals single 7. Calabaria, p. 92. 



II. No supraobital bone ; no preemaxUlary teeth ; subcaudals 

 mostly single BOIN^. 



A. Head distinct from neck ; tail more or less prehensile. 



1. Anterior teeth very strongly enlarged. 



Scales smooth ; head with shields ; labials without or with shallow 

 pits 8. Epicrates, p. 93. 



Scales smooth ; labials with deep pits. 9. Corallus, p. 99. 



Scales keeled ; no labial pits 10. Enygrus, p. 104. 



2. Maxillary and mandibular teeth gradually decreasing in 



size, 



a. No enlarged rostral shield ; scales strongly keeled. 



11. Trachyboa, p. 109. 



b. An enlarged rostral shield. 



a. Scales moderate, in 21 to 29 rows. 

 One or two pairs of praefrontal shields. 12. Ungalia, p. 110. 

 A large azygous preefrontal shield 13. UngaliopMs, p. 114. 



/3. Scales very small. 



Scales smooth ; nasals in contact behind the rostral. 



14. Eunectes, p. 115. 



Scales smooth ; nasals separated by small scales ; tail short. 



15. Boa, p. 116. 



Scales keeled ; nasals separated by a pair of internasals ; tail long. 



16. Casarea, p. 121. 



B. Head not distinct from neck ; tail not or but slightly 



prehensile. 



1. Scales tri- or quinquecarinate ; snout with large shields; 

 rostral moderate 17. Bolieria, p. 121. 



