The white-ankled mouse is commonly found in coexistence with the brush mouse and Texas mouse ("P. boylii" and "P. attaweri", respectively). Often, the sympatric overlap in characteristics between these species makes it difficult to identify a specific species. The most distinguishing feature of the white-ankled mouse, and the one most used to identify the species, is the baculum of males (Hooper 1958). The tip of the white-ankled mouse’s baculum is long and cartilaginous, whereas the tips of brush and Texas mice are short and rounded (Clark 1952 and Hooper 1958).