CHECKLIST OF THE SNAKES OF MEXICO 13 



13. Number of scale rows in front of anus equal to or only one less than 



number at middle of body 14 



Number of scale rows in front of anus at least two less than number 



at mldbody 60 



14. Scale rows 13 15 



Scale rows 15 or more 17 



15. Internasals fused with anterior section of nasal; rostral enlarged; 



snout produced beyond lower jaw, sharp-edged, rounded in dorsal 



profile, pointed in lateral profile Chilomeniscus (p. 34) 



Internasals not fused with anterior section of nasal; snout not pro- 

 duced forward, shovellike 16 



16. Body with black rings ; 2 anterior temporals ; ventrals 168 ; size 



larger Bipsas' (p. 49) 



Body uniform brown above ; 1 anterior temporal ; ventrals 126-128. 



Sonora' (p. 126) 



17. Rostral in contact with frontal Ficimia (p. 62) 



Rostral separated from frontal 18 



18. Scales in 19 rows 19 



Scales in 15 or 17 rows 20 



19. Internasals fused with prefrontals ; scales smooth Sympholis (p. IM) 



Internasals distinct from prefrontals; scales keeled Ninia (p. 99) 



20. Rostral in contact with prefontals Gyalopion (p. 70) 



Rostral separated from prefrontals 21 



21. Anal single 22 



Anal divided 32 



22. Prefrontals fused to form a single, large scale ; black above with a yellow 



nuchal collar ; scales feebly keeled ; no preoculars — Chersodrom.us (p. 33) 

 Prefrontals separate ; color not as described ; scales keeled or not ; pre- 

 oculars present or not 23 



23. Scale rows 15 26 



Scale rows 17 24 



24. No preocular ; eye small ; small, burrowing snakes with pointed head. 



Geophis (part) (p. 65) 

 One or two preoculars ; size larger ; eye larger ; head not reduced for 

 burrowing ^^ 25 



25. Two superimposed anterior temporals Clelia (p. 35) 



One anterior temporal Tropidodipsas (part) (p. 149) 



26. No anterior temporal and no preocular ; small, burrowing snakes with 



pointed heads Geophis (part) (p. 65) 



An anterior temporal present or, if lacking, preoculars present 27 



27. Five supralabials ; two preoculars ; no loreal ; anterior temporal present 



or absent Adelophis (p. 153) 



Six or more supralabials ; preoculars variable ; loreal variable ; temporals 

 normal 28 



28. Nasal entire ; vertebi'al scales not enlarged ; no azygous scale behind 



mental ; presumably no loreal (not certain) Exelencophis (p. 62) 



Nasal divided or, if entire, either the vertebral scales are enlarged or 

 there is an azygous scale behind mental ; loreal present 29 



29. Six upper labials; dorsal scales with two apical pits Geatractus (p. 64) 



Seven or more upper labials ; dorsal scales without pits 30 



'Dipsas gaigeae (Oliver) only. 

 * Sonora taylori (Boulenger) only. 



584960 — 45—2 



