REPTILES 



199 



Ci Subcaudals undivided, forming a single row; scales on 



chin all small 2. Boidce. 



02 Subcaudals divided, forming 2 rows (except in Kliino- 

 cheilus) ; one or two pairs of enlarged elongate shields 



on the middle line of the chin 3. Cohtbridce. 



bo Elongate poison fangs present in front part of mouth. 



Ci Head not distinct from neck; no pit between eye and 



nostril 4- Elapidce. 



Co Head very distinct; a pit between eye and nostril (Fig. 



127) 5. Crotalid<B. 



'9 



5T 5 



Fig. 115. — Head of snake {Coluber constrictor) showing the plates: i, frontal; 2, parietals 

 3, supraoculars; 4, prefrontals; 5, internasals; 6, preoculars; 7, loreal; 8, postocular; 9, ros- 

 tral; 10, upper labials; 11, temporals; 12, nasals; 13, lower labials {from Hay). 



Family i. Leptotyphlopidae. — Small, blind, worm-like snakes 

 with rudiments (not visible) of hind legs and a pelvic girdle: i genus 

 and 3 species in the United States. 



