The Opitthoglyph Snakes of North America 



seized, is worked quickly backward into the mouth by alternate, 

 grasping movements of the jaws, until the fangs are firmly im- 

 bedded, and in this position it is held until all struggles have 

 ceased, when it is swallowed. The prey is generally benumbed 

 and helpless within one or two minute's time. After a period 

 of about five minutes it appears to be quite dead. The bitten 

 creature seems to die with the muscles perfectly relaxed and in 

 this condition is easily swallowed by the snake as the limbs fold 

 readily against the body during the progress of the snake's jaws 

 over it. To observe one of these snakes feeding is to appreciate 

 the existence of an excellent development for the overpowering 

 of the reptile's prey. 



Though jt has not hitherto been the custom, the writer 

 without hesitation classes the Opistboglypba among the poisonous 

 snakes, and would advise the student to discriminate between 

 living examples of these reptiles and the wholly innocuous snakes 

 they so closely resemble. 



An outline of the North American genera follows:* 



I. Pupil elliptical. 



Si^e moderate. 



Body rather slender; head flat, wide and very distinct 



from the neck. 

 Colouration. Pale, with darker blotches. 



Two loreal plates. Trimorphodon. 



Distribution. Southwestern United States; Mexico 



and Central America. 



Conformation and colouration similar to preceding genus. 

 One loreal plate. Sibon. 



Distribution. Texas, Mexico and Central America. 



II. Pupil round. 

 Si^e small. 



Body moderately slender. Head but slightly -distinct. 

 Pattern (of local species) in bands extending lengthwise. 



Erythroiamprus . 

 Distribution. Texas, Mexico, Central and South 



America. 

 Si^e very small. 



Body moderately slender; head not distinct. Body 



brown; head blackish. Tantilla. 



Distribution. Southern United States from South 



Carolina to California; Mexico, Central America 



and South America. 



*The species of all the genera have smooth scales. 



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