Beals, Ralph L. "Southern Mexican Highlands and Adjacent Coastal Regions." In Ethnology, Part 1, edited by Robert Wauchope and Evon Z. Vogt, 315. Vol. 7 of Handbook of Middle American Indians. Austin: University of Texas Press, 1969. https://ebookcentral-proquest-com.proxy.library.upenn.edu/lib/upenn-ebooks/reader.action?docID=4826335&ppg=333