178 COLTJBBIDJE. 



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



8. Xenochropliis, p. 191. 



2. Maxillary teeth minute posteriorly, much 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 internasal shields. 



a. Scales forming longitudinal series throughout the body. 



Maxillary teeth 18 to 40, forming a continuous series. 



10. Tropidonotus, p. 192. 



MaxUlary 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 l?rge 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. 



Maxillary teeth 20 to 28 13. Pseudoxenodon, p. 270. ■ 



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



with round pupil ; a single internasal shield. 



Mandibular teeth subequal ; nostril in a seinidivided nasal ; scales 

 without pits 14, ' Helicops, p. 272. ' ■' 



Mandibular teeth decreasing in size posteriorly ; nostril between two 

 nasals; scales with apical pits , . 15,'HydraBtIuops, p. 280, /;.', 



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



terior somewhat enlarged ; eje 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 proeocular ; nostrils on upper surface 

 of snout. 

 Maxillary teeth strong, about 30 .. 16. Tretanorhinus, p. 281, 

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



** Scales keeled ; one or two prseoculars ; nostrils 

 lateral. 



Maxillary teoth 14 to 18 18. Ischnognathus, p. 285. 



