Tropidoclonion is a genus of snake in the subfamily Natricinae of the family Colubridae. The genus is monotypic, containing the sole species Tropidoclonion lineatum, commonly known as the lined snake. The species is endemic to North America.
Additional common names for T. lineatum include common snake, dwarf garter snake, grass snake, line snake, ribbon snake, streaked snake, striped snake, and swamp snake.
The subspecific name, mertensi, is in honor of German herpetologist Robert Mertens.
The lined snake is olive green to brown with a distinctive tan or yellow stripe running down the middle of the back from head to tail. It has similar stripes, one down each side on scale rows 2 and 3. On the belly, it has a double row of clean-cut black half-moon spots running down the middle. It has a narrow head and small eyes.
Adult size is typically less than 35 cm (14 inches) in total length (including tail). However, maximum recorded total length is 53 cm (21 in).
The keeled dorsal scales are arranged in 19 rows at midbody. There are only 5 or 6 upper labials.
The lined snake is found throughout the central United States from Illinois to Texas.
The preferred habitat of T. lineatum is grassland areas with soft, moist soils.
The lined snake is semifossorial, spending most of its time hiding under rocks, leaf litter, logs, or buried in the soil.
The majority of the diet of T. lineatum consists of earthworms.
The lined snake is ovoviviparous, the young being born in August. The average brood is seven or eight. The newborn juveniles are 10–12 cm (4-4¾ in.) long at birth.
