We studied the eight species of Crotalus inhabiting the Mexican state of Hidalgo and found additional variation involving number of scales, body length, and distribution previously unreported in the literature. Supplementary morphological variation is reported for C. aquilus and C. atrox, and new distributional records are reported for C. aquilus, C. atrox, C. intermedius, C. scutulatus, and C. totonacus.
