Regional Morphology

This is relevant for Pit Vipers in North America.

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 sp.
no		no

		Crotalus sp.


Are there several enlarged shields on the top of the head (generally 9)?	yes			Agkistrodon sp.