Western cottonmouth

The dark back of this snake is not well patterned, except in juveniles. The dorsal scales are weakly keeled. The pupils are vertical slits. The head is visibly wider than the neck. There is a dark stripe from the neck through the eye and up to the tip of the snout, this is most easily seen in juveniles. There is a heat sensing pit between (but below) the eye and nostril on either side of the face. There is a white line on the upper lip. The ground color of the belly is light, but the belly has many large dark blotches that make it look dark. There is a single row of scales under the tail, a single anal plate, and no rattle. The neonate has a yellow to yellow-green tail tip. (information from "A Field Guide to Amphibians and Reptiles of Oklahoma")