Adults averages between 40 to 70 cm in total length (body + tail), with a maximum total length of 108 cm being reported. Females are usually larger than males. These snakes can attain a considerable weight relative to their size, with specimens sometimes exceeding 500 g.The head is broad, flat, distinct from the neck and covered with small, imbricate scales. The snout is short and rounded. The nostrils are positioned dorsolaterally and have valves. The nasal scale is unbroken. The rostral scale is small and wide. The eyes are small to average in size. There are 15-20 interocular scales and 15-20 circumorbitals. The supraorbital hornlike structure above each eye consists of small, imbricate scales and is also present in juveniles. There are 11-14 supralabials and 13-17 sublabials. 2-4 rows of small scales separate the supralabial scales from the suboculars. The body is covered with weakly to strongly keeled dorsal scales. On many of these, the keel terminates before the end of the scale and forms a bump. Many others form a point. At midbody, there are 21-25 scale rows, none of them oblique. There are 134-163 ventral scales and 35-50 paired subcaudals. The tail is short.