In the racer the maxillary, palatine, pterygoid, and dentary bones bear teeth (Fig. 1). The teeth are all much alike in size and shape, small, sharp, and recurved, typically at an angle of approximately 50 degrees. The number of teeth present is variable. Because the teeth are small and loosely attached to the jaw bones, and often are broken off in the capture and ingestion of prey, each bone usually lacks part of its complement of teeth. Even the sockets vary somewhat in number between individuals, and between the left and right sides in some snakes. Most of the skulls that I examined were not thoroughly cleaned, and the adherent dried tissues made it difficult to obtain accurate counts of the sockets. In ten skulls from Kansas and Nebraska, most frequently occurring numbers of sockets for each of the dentigerous bones were: maxillary, 15; palatine, 11; pterygoid, 18; dentary, 18. [Illustration: Fig. 1. Lateral view of right side of skull of adult female blue racer, × 4. University of Kansas Museum of Natural History no. 18305, from Greenwood County, Kansas.] _Hemipenis_ Penial characters have proven to be useful in the classification of snakes, providing bases for separating subfamilies, genera, and species. In the racer even the subspecies have trenchant penial characters by which they may be separated in some instances. The hemipenis is roughly cylindrical, but widest at the base (Fig. 2). The sulcus spermaticus is unbranched. Approximately the basal one-third of the hemipenis has a smooth surface, broken only by the sulcus spermaticus and by three greatly enlarged spines, which form hooks--one anterior, one posterior, and one dorsal. The dorsal hook is the largest of the three. Distal to the smooth part is a zone of small spines, each recurved and mounted on a fleshy tubercle. The zone of spines is poorly developed on the anterior side and is interrupted on the posterior side in the vicinity of the sulcus spermaticus but is best developed on the posterior side a short distance above and below the sulcus spermaticus. The spines are arranged in several oblique rows. Those of the proximal row are best developed, and there is rapid diminution in the size of those situated farther distally. Approximately the distal two fifths of the hemipenis forms a third zone, lacking distinct spines, but having numerous deep longitudinal grooves, alternating with lamellae which have fimbriated edges, and which fuse with each other and divide to form a reticulated pattern. [Illustration: Fig. 2. Lateral view of injected and everted left hemipenis (slightly enlarged) of a blue racer from the Rockefeller Tract, Jefferson County, Kansas, showing heavy spines at base of organ, small spines of central zone and lamellae of terminal part. This hemipenis is not fully engorged.] Relationships