I gratefully acknowledge the generous help of Professor A. Byron Leonard, under whose guidance this study was conducted and thank Professor E. Raymond Hall, Professor Howard A. Matzke, and Dr. Irwin Baird for numerous helpful suggestions and criticisms. For help in collecting specimens I thank J. R. Alcorn, W. C. Glazener (through the courtesy of the Texas Game and Fish Commission), Dr. Harrison B. Tordoff, Jerry Tash, William Brecheisen, and Louis Brecheisen. I thank also Edwin Gebhard of the Kansas Forestry, Fish and Game Commission for help in locating the Lesser Prairie Chickens. I am grateful for the assistance of Mrs. Chester Alexander and Dr. L. C. Dahl in translating a Russian and a Dutch reference, and thank George Young and James Bee for making equipment used in my study. All of the original drawings except fig. 1 were made by me, although the final inking of figs. 12 through 19 was done by Bret Waller. Fig. 1 was drawn by Kay Swearingen. I was aided in this study during the summer of 1960 by a research grant from the University of Kansas. SKELETON Although no special study was made of the skeleton, certain conspicuous variations are discussed here. There are a few pronounced differences between the pelvis of _Tympanuchus_ and that of _Pedioecetes_. Whereas in the former the thick lateral iliac process has a pronounced overhang with the ventral edge lateral to the ischium (fig. 1), in _Pedioecetes_ there is no overhang at all and the edge of this process is much thinner. The ischium in _Pedioecetes_ is wider (in dorsoventral extent), especially posteriorly, than in _Tympanuchus_. In _Tympanuchus_ the posteroventral margin of the ischium is rounded and is free from the pubis, whereas in _Pedioecetes_ it is pointed and fused with the pubis. In _Tympanuchus cupido_ (both subspecies) the lateral iliac process extends farther ventrally than in _T. pallidicinctus_, approaching or extending ventral to the level of the pubis in the former species; also the edge of this process is thicker in _T. cupido_. All specimens studied have a single synsacro-thoracic vertebra. The number of combined synsacro-thoraco-lumbar and synsacro-lumbar vertebrae is eight in each specimen of _Tympanuchus_ and in one specimen of _Pedioecetes phasianellus jamesi_ and is seven in three specimens of the latter. In most specimens of _Tympanuchus_ there are three synsacro-thoraco-lumbar and five synsacro-lumbar vertebrae, although in two specimens (_T. pallidicinctus_) there are four of each group; in one of these latter two specimens the parapophysis on one side of the fourth synsacro-thoraco-lumbar vertebra is small. The first (of five) synsacro-lumbar vertebra has a rudimentary parapophysis on one side in one specimen of _Tympanuchus_ and on both sides in another specimen. One specimen of _Pedioecetes phasianellus jamesi_ has five synsacro-lumbar vertebrae and the others have four; all have three synsacro-thoraco-lumbar vertebrae. NERVES