Scalation that of typical colubrid (see [Pl. 19]); rostral large, extending back onto dorsal surface of snout, bluntly pointed behind; paired internasals considerably wider than long, convex anteriorly, almost straight-edged posteriorly, each extends laterally to naris; paired prefontals approximately twice size of internasals, and wider than long, extending laterally on each side to level of nostril; frontal convex anteriorly, concave on each side, bluntly pointed behind, nearly twice as wide anteriorly as posteriorly; parietals large; angle formed between them by frontal slightly more than 90 degrees; nostril large, situated between almost equal sized anterior nasal and posterior nasal plates; loreal slightly smaller than nasals, its anterior edge inclined forward superiorly; two rows of temporals on each side; in upper row, first one narrow and elongate, second much shortened, third intermediate in shape; in lower row all three approximately alike in size and shape; two postoculars, the lower larger; seven supralabials, first small and low, longer along upper edge than along lower, second slightly longer than high, third higher than long, contacting eye; fourth largest, contacting posterior part of eye, and lower postocular; fifth nearly as large, pointed above; sixth also large, pentagonal; seventh low and rectangular; on chin first pair of infralabials separate mental from anterior genials; second infralabial minute; third approximately twice its size; fourth much smaller, rhomboidal, fifth also large, pentagonal; sixth smaller, rhomboidal, bluntly pointed behind; seventh smaller, narrow behind; eighth small and elongate; second pair of genials longer and narrower than those of first pairs, separated from each other by smaller scales; genials in approximately five rows, but somewhat irregular in arrangement, mostly smaller and narrower than body scales; latter all smooth, arranged in 17 rows for about two-thirds of body length, then, by loss of third row on each side, reduced to 15; scales of neck region rounded and relatively small, one-third to one-fourth size of larger body scales; lowest scale row on each side largest with its scales much wider and less symmetrical than others; most of body scales of approximately hexagonal shape; on forebody they average approximately twice as long as wide, but farther posteriorly on body, width-length ratio gradually increases and some of scales, notably those of lowest row, approximately as wide as long; regularity of scale rows broken on sides just above vent by presence of many small additional scales; on tail scale rows drop out posteriorly in rapid succession, until on posterior third only four are present; ventrals strongly convex posteriorly, with free posterior edges, nearly half length of scales; anal plate divided, with diagonal suture; subcaudals in double series, those of right and left sides alternating; several minute subcaudal-like scales on each side of vent.
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.
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.
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.