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Morphological identification key

Crotalinae  
             

Is there a "rattle" or a knob-like projection on the end of the tail?

yes
 

Are there several enlarged shields on the top of the head (generally 9, sometimes 11)?

yes  

Sistrurus catenatus,

Crotalus ravus
no     no      
             
    Crotalus sp.(excluding Crotalus ravus)      
         

Are there several enlarged shields on the top of the head (generally 9)?

yes

  Agkistrodon sp.
           
no
         
           

Are there protruding, spiky scales underneath the tip of the tail?

yes   Lachesis sp.
 
no
         
             

Are there characteristic markings in the form of open triangles or arrowheads?

yes   Bothrops asper
 
no
           
             

Atropoides sp.

Bothriechis sp.

Cerrophidion sp.

Mixcoaltlus sp.

Metlapilcoatlus sp.

Ophryacus sp.

Porthidium sp.