It is the posterior border of the retropharyngeal space.

The head shows two small black spot, respectively in the middle of the anterior and the posterior border.

The posterior border is free, concave, and separates the choanae.

The inner surface of the ear is almost bare except for a dusky spot on the posterior border.

The posterior border is concave, free, and serves for the attachment of the soft palate.

There are no projecting triangular scales on the posterior border of the head.

The head is black, the black extending to the posterior border of the parietals.

Choanae are behind the line of the posterior borders of the orbits.

The lobes have three different types: anterior, posterior and inferior borders.

Pygidium has a long, narrow axis of 10 rings, virtually reaching the posterior border.