178 COITTBEID^. 



Scales keeled, without pits ; nostril in a single nasal. 



8. Xenochrophis, p. 191. 



2. MaxiUary teeth minute posteriorly, muoh larger ante- 



riorly ; eye rather large, with round pupil. 



Scales keeled 9. Prymnomiodon, p. 192. 



3. Posterior maxillary teeth longest; mandibular teeth sub- 



equal ; eye moderate or large, with round pupil ; a pair 

 of intern asal shields. 



a. Scales forming longitudinal series throughout the body. 



Maxillary teeth 18 to 40, forming a continuous series. 



10. Tropidonotus, p. 192. <^ 



Maxillary teeth 14 to 22, the last two very large fangs separated 

 from the rest by an interspace ; snout rounded ; scales keeled. 



11. Macropisthodon, p. 265. 



Maxillary teeth 12 to 14, the last two very large fangs separated 

 from the rest by an interspace ; snout pointed, projecting ; scales 

 smooth 12. Lioheterodon, p. 268. 



h. Scales disposed obliquely on the anterior part of the 

 body. 



MaxUlary teeth 20 to 28 13. Pseudoxenodon, p. 270. 



4. Posterior maxillary teeth longest ; eye moderate or small, 



with round pupil; a single intemasal shield. 



Mandibular teeth subequal ; nostril in a semidivided nasal ; scales 

 without pits 14. Helicops, p. 272. 



Mandibular teeth decreasing in size posteriorly ; nostril between two 

 nasals ; scales with apical pits . . 15. HydrsBthiops, p. 280. 



5. Maxillary teeth subequal ; mandibular teeth equal or an- 



terior somewhat enlarged ; eye small or rather small, 

 with round or vertically elliptic pupil. 



a. Labial shields not entering the nostril ; subcaudals in two 

 rows. 



a. Maxillary bone extending forwards beyond the pala- 

 tines. 



* Scales keeled ; a prseocular ; nostrils on upper surface 

 of snout. 



MaxiUary teeth strong, about 30 . . 16. Tretanorhinua, p. 281. 



Maxillary teeth small, 20 to 25 . . 17. Opisthotropis, p. 283. 



** Scales keeled ; one or two prseoculars ; nostrils 

 lateral. 



Maxillary teeth 14 to 18 18. Ischnognathus, p. 285. - 



