"A New Piñon Mouse (Peromyscus truei) from Durango, Mexico" by Robert B. Finley, Jr. is a scientific publication written in the early 1950s. This work is focused on the documentation and classification of a newly identified subspecies of piñon mouse found in Durango, Mexico. It presents detailed morphological characteristics that differentiate this subspecies from its relatives in adjoining areas. The book discusses the findings from a collection of specimens collected by J. R. Alcorn, highlighting the darker pigmentation of the newly identified piñon mouse, designated as Peromyscus truei erasmus. The text outlines the physical traits, habitat, and geographic range of this subspecies, emphasizing its evolutionary adaptations to the surrounding rocky environment. Finley meticulously compares this mouse to others in the Peromyscus genus, providing measurements and diagnostic features that confirm its status as a distinct subspecies. Overall, the publication contributes to the understanding of mammalian diversity in Mexico and emphasizes the role of natural selection in shaping species characteristics. (This is an automatically generated summary.)