What physical characteristic defines the snakes referred to as 'keelbacks'?

Answer

A dorsal ridge causing the scales to feel raised or keeled

The name 'keelback' directly describes the physical feature of a dorsal ridge running down the snake's back, resulting in scales that are keeled rather than smooth.

What physical characteristic defines the snakes referred to as 'keelbacks'?
ToxicityvenomreptilesnakeKeelback