"Records of the Fossil Mammal Sinclairella, Family Apatemyidae, From the Chadronian and Orellan" by William A. Clemens, Jr. is a scientific publication written in the early 1960s. The book presents a detailed examination of fossil specimens belonging to the family Apatemyidae, focusing specifically on the genus Sinclairella. The content delves into the geological and evolutionary significance of these mammals during specific land-mammal ages. The publication documents the findings of various fossil specimens of Sinclairella dakotensis from Chadronian and Orellan strata in the United States, notably from locations in South Dakota, Nebraska, and Colorado. Clemens provides comprehensive descriptions and comparisons of the teeth and other skeletal remains, enhancing the understanding of the Apatemyidae's evolutionary history. By analyzing the morphology and stratigraphy of these fossils, the author establishes connections between different fossil sites and extends the known geographic and temporal range of the family, contributing to the broader field of paleontology. (This is an automatically generated summary.)