head shape
posterior margin flat
posterior margin flat 
The posterior margin of the head flat. Used in Antkey to separate the minor worker of Pheidole teneriffana from Pheidole obscurithorax (strongly convex) and Pheidole fervens (weakly convex).
posterior margin weakly concave
posterior margin weakly concave
The posterior margin of the head weakly concave to flat, but never strongly convex. Used in Antkey to separate Plagiolepis exigua from Plagiolepis alluaudi and Plagiolepis pygmaea.
posterior margin relatively flat
posterior margin relatively flat
The posterior margin of the head generally flat and broad before arching towards eyes. Used in Antkey to separate Pheidole bilimeki from Pheidole anastasii and Pheidole
posterior margin relatively narrow
posterior margin relatively narrow
The posterior margin of the head generally convex and narrow before arching towards the eyes. Used in Antkey to separate Pheidole punctatissima from Pheidole bilimeki and Pheidole anastasii.
posterior margin weakly convex
posterior margin weakly convex
The posterior margin of the head weakly convex. Used in Antkey to separate the minor worker of Pheidole fervens from Pheidole obscurithorax (strongly convex) and Pheidole teneriffana (flat).
posterior margin flat
posterior margin flat
The posterior margin of the head is generally flat and lacks a median impression. Used in Antkey to separate Tetramorium simillimum from Tetramorium caldarium. This character is based on examination of limited material, however, and requires further study before its usefulness can be verified.
posterior margin weakly concave
posterior margin weakly concave
The posterior margin of the head is weakly impressed medially. Used in Antkey to separate Tetramorium caldarium from Tetramorium simillimum. This character is based on examination of limited material, however, and requires further study before its usefulness can be verified.
head ovoid
head ovoid
head ovoid (Pheidole)
head shape rectangular
head shape rectangular
head shape rectangular (Pheidole)
head shape square
head shape square
head shape square (Pheidole)