Lacunolabial scale

The lacunolabial scale is a large scale that forms in some crotaline snakes (pitvipers) when the prelacunal scale fuses with the second (rarely the third) supralabial scale.

[1][2] In such cases, it is often said that "the second labial enters the pit".

[3] Some pitvipers, such as Bothrops alternatus, Bothrops erythromelas, Bothrops itapetiningae and Bothrops neuwiedi, have a divided lacunolabial scale.

[4]