[1] Commonly referred to as spinejaw snakes, this genus is found in Borneo and peninsular Malaysia.

This genus is taxonomically and phylogenetically challenging to classify, as these snakes possess several morphological traits that distinguish them from all other snake species; head scales with numerous sensory papillae, large prefrontal scales, and an upper jaw that has a spiny palatine process.

They also lack any pelvic girdle vestiges, a left lung, or a coronoid bone.

[2] In 2004, cytochrome b sequencing suggested a sister relationship of Xenophidion to Bolyeriidae from Mauritius.

[3] Similar to Boyleriidae, spinejaw snakes have a jointed maxilla.