Produced by Chris Curnow, Tom Cosmas, Joseph Cooper and the Online Distributed Proofreading Team at http://www.pgdp.net UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY Volume 9, No. 23, pp. 579-670, 4 pls., 12 figs. in text June 16, 1960 Speciation and Evolution of the Pygmy Mice, Genus Baiomys BY ROBERT L. PACKARD UNIVERSITY OF KANSAS LAWRENCE 1960 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman, Henry S. Fitch, Robert W. Wilson Volume 9, No. 23, pp. 579-670, 4 pls., 12 figs. in text Published June 16, 1960 UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED IN THE STATE PRINTING PLANT TOPEKA, KANSAS 1960 [Illustration: Look for the Union Label] 28-3030 Speciation and Evolution of the Pygmy Mice, Genus Baiomys BY ROBERT L. PACKARD CONTENTS PAGE Introduction 583 Materials, Methods and Acknowledgments 584 Paleontology of the Genus 587 _Baiomys sawrockensis_ 588 _Baiomys rexroadi_ 589 _Baiomys kolbi_ 590 _Baiomys brachygnathus_ 590 _Baiomys minimus_ 591 Phyletic trends 592 Non-Geographic Variation 595 Variation with age 595 Secondary sexual variation 597 Individual variation 597 Pelage and molts 598 Taxonomic Characters and Relationships 600 External parts 600 Pelage 600 Skull 600 Teeth 601 Hyoid apparatus 601 Baculum 603 Auditory ossicles 605 Genus Baiomys 607 Systematic Accounts of Species and Subspecies 608 _Baiomys musculus_ 608 _Baiomys musculus brunneus_ 612 _Baiomys musculus grisescens_ 614