Thamnophis proximus

Thamnophis proximus, commonly known as the western ribbon snake, is a species of garter snake in the subfamily Natricinae of the family Colubridae. The species is endemic to the western United States, Mexico, and Central America. The species has six recognized subspecies.
Description.
"T. proximus" is a slender snake with a very long tail, approximately one-third of the total length of the body. Dorsally, "T. proximus" is blackish, brown, or olive with three light-colored stripes. Ventrally, it is greenish-white or yellowish-white. The upper labials are whitish and unmarked, contrasting with the dark top and sides of the head.
Adults measure in total length (including the tail).
Subspecies.
Six subspecies of the western ribbon snake ("T. proximus") are recognized as being valid, including the nominate subspecies.
"Nota bene": A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than "Thamnophis".