"A New Subspecies of Lizard, Cnemidophorus sacki, from Michoacán, México" by William E. Duellman is a scientific publication written in the mid-20th century, specifically in the early 1960s. This work focuses on the systematic study and classification of a newly identified subspecies of the lizard Cnemidophorus sacki found in Michoacán, Mexico. It contributes to the field of herpetology by providing detailed descriptions and distinguishing characteristics of this subspecies. In the publication, Duellman describes the distinctive features of the Cnemidophorus sacki zweifeli, elaborating on its size, coloration, and morphological differences compared to other subspecies. The study includes a holistic examination from field studies, discussing habitat preferences, variations in size and color, and sexual dimorphism. Additionally, the lizard's ecological behavior during different seasons and its geographic distribution within the Tepalcatepec Valley is thoroughly analyzed. The work not only provides insights into this particular subspecies but also highlights the importance of taxonomy and field research in understanding biodiversity. (This is an automatically generated summary.)