Hi Roger, Aphaenogaster and Pheidole generally look quite similar and are in the same subfamily (Myrmicinae). The body shapes are slightly different (head shape, the curve on the back of the body, the shape and orientation of the spines) and the antennae are different - Pheidole has a "club" at the end of the antenna which has three large segments (which you can just see in your photos) while Aphaenogaster has a four-segmented club. Cheers, Jon