Part 4

+ 7(26) 6 + 7(38) +7(39) 14 ---------- 15 ---------- 14 ------------ 13---------- 14----------, 6 + 7(36) +7(42)

15 --------- 14 ---------, -6(45) +7(53)

7 + 8(67) + 7(69) 15 ------------ 14 ----------- 15 ----------- 14 ---------- 15----------, 6 + 7(90) +7(93) 6 + 7(99)

14 ------------ 15(122). + 7(100)

Specimen 83620 is the only one for which we have determined the complete dorsal scale formula. Obviously the formula is complex, and possibly the specimen is atypical in this regard. Nevertheless, addition and reduction of scale rows is apparent on other specimens and can be easily observed by examining specimens under a dissection microscope.

Anal plate

Of the 246 specimens examined, 232 (94.3%) have the anal plate divided. Of the 14 specimens having undivided anal plates, four have an incomplete groove anteriorly in the plate.

Ventrals

Females have from 122 to 137 (mean, 130.8 +- 0.26; N = 107) ventrals; males have from 117 to 131 (mean, 122.3 +- 0.21; N = 139; Fig. 2). Of the 246 specimens examined, 29 (11.8%; 11 females and 18 males) have an added half-ventral immediately anterior to the anal plate. Of these specimens, 27 have the added half-ventral on the left side and two have it on the right. Five specimens have the last ventral divided similar to the normal division of the anal plate. One specimen has the last ventral incompletely divided transversely. Excluding the last ventral, seven specimens have divided ventrals (half-ventrals). Four of these specimens have added half-ventrals on the right side (two specimens with one half-ventral each, one specimen with two half-ventrals, and one specimen with three half-ventrals), and four have added half-ventrals on the left side (one half-ventral on each specimen).

Subcaudals

Females have from 37 to 47 (mean, 42.0 +- 0.20; N = 79) subcaudals; males have from 43 to 55 (mean, 48.4 +- 0.23; N = 109; Fig. 3). Of the 187 specimens examined, 13 (7.0%) have the last pair of subcaudals fused. One specimen has left subcaudal 28 fused with both adjacent subcaudals (also fused) on the right. While reading proof we found two omissions in Fig. 3; there should be illustrated two males with 43 subcaudals and three males with 44 subcaudals.

Ventrals minus subcaudals

The value for number of ventrals minus the number of subcaudals varies from 80 to 96 (mean, 88.8 +- 0.39) for 79 females, and from 67 to 83 (mean, 73.8 +- 0.28) for 109 males.

Additional scale characteristics

Of the 246 specimens examined, four (1.6%) have the rostral in contact with the left prefrontal, and hence the internasals are separated from one another. One snake has approximately one-fourth (anteriorly) of the suture between the parietals fused. One specimen has the posterior edge of the frontal fused with the left parietal. One specimen has the parietal shield on the right side abbreviated posteriorly. One specimen has both prefrontals fused with the frontal, although an incomplete suture is present.

Maxillary characteristics (Figs. 4 and 5)

Maxillary teeth anterior to fangs 10-14 (mean, 12.1; N = 20); tooth-socket number 6.5-8.5 (mean, 7.2; N = 20) directly opposite distal tip of suborbital process; lateral anterior foramina 1-3 (mean, 1.8; N = 20); tooth number 6-9 (mean, 6.9; N = 12) directly below center of posterior foramen (if only two foramina present). Three specimens lack a diastema and 17 specimens have a diastema. The anterior and posterior edges of the suborbital process are parallel in two specimens and not parallel in 14; the process is broken in four specimens. The lengths (anterior to posterior) of the lateral anterior foramina (if only two are present) are approximately equal in six specimens, and in six the anteriormost one is the longest; six specimens have one foramen and two specimens have three foramina. All specimens examined have two fangs, with the posterior edge of the lateral flange forming an obtuse angle.

Discussion and Conclusions

Generic characteristics of Tantilla are as follows: size small, body slender, head not noticeably distinct from body; preoculars one; postoculars one or two; nasals two; loreal absent; smooth dorsal scales in 15 rows; anal plate usually divided but sometimes single; subcaudals paired; usually two enlarged, posterior, grooved fangs on the maxilla separated by a small diastema from the other maxillary teeth (Baird and Girard, 1853:131; Cope, 1900:1110; Dunn, 1928:24; Blanchard, 1938:369; Schmidt and Davis, 1941:268; Wright and Wright, 1957:722; Conant, 1958:180). Of these characteristics, only the following were invariable in our sample: size small, body slender, head not noticeably distinct from body; postoculars one or two; smooth dorsal scales; posterior grooved fangs on maxilla. The dorsal scales, anal, and subcaudals were "correct" 92 per cent of the time; the preoculars and nasals were "correct" 97 per cent of the time.

Tantilla reportedly has two nasals (Baird and Girard, 1853:131; Cope, 1900:1110; Wright and Wright, 1957:722). Tantilla gracilis usually has a single nasal that is divided below the naris; variation in this characteristic is discussed above.

In addition to the generic characteristics, specific characteristics for T. gracilis are as follows: supralabials 5-8 (usually 6); supralabials 3 and 4 entering orbit; infralabials 5-7 (usually 6); temporals 1 + 1; ventrals 115-138 in females, 106-132 in males; subcaudals 33-53 in females, 40-57 in males; tail length 13-27 per cent total length in females, 15-30 per cent in males (Baird and Girard, 1853:132; Cope, 1900:1111-12; Force, 1935:653-54; Taylor, 1936:337-38; Blanchard, 1938:371-72; Kirn, Burger, and Smith, 1949:240-49). Excepting the number of temporals and the supralabials entering the orbit, the characteristics of the specimens in our sample are within the ranges of variation mentioned above. Of the 10 maxillary characteristics studied, no variation was observed in number of fangs or angle of lateral flange.

Because our data have some bearing on the problem of geographic variation in T. gracilis and the recognition of subspecies, we comment briefly on the status of subspecies in T. gracilis. Kirn, Burger and Smith (1949) proposed the recognition of two subspecies of Tantilla gracilis (T. g. gracilis Baird and Girard and T. g. hallowelli Cope). These subspecies were diagnosed on the basis of differences in ventrals, subcaudals, and the ratio of tail length to total length; sexual dimorphism in each characteristic was considered. We do not recognize these subspecies for the reasons given below.

The data of Kirn et al. (1949) appear to be presented inaccurately in part. Both of us independently recalculated the mean given for each characteristic for each subspecies, using the data in figures 2-4 of Kirn et al. (1949:242, 244-245). Of their 12 means presented (table 1, p. 247) only two agree with our recalculated means, although the means calculated by each of us independently are in complete agreement (Table 5). Also, we independently calculated the percentages of specimens of each "subspecies" that are included in the ranges of variation given in their diagnoses (Table 5); again, our independent calculations are in complete agreement. In our opinion the differences between the populations for the characteristics analyzed do not warrant recognition of subspecies (Fig. 6).

TABLE 5. Means of "Diagnostic" Characteristics of T. g. gracilis Baird and Girard and T. g. hallowelli Cope.

============================================================================= | T. g. gracilis | T. g. hallowelli -----------------+-----------------------------+----------------------------- | | |Per cent | | |Per cent CHARACTERISTICS | | Mean |specimens | | Mean |specimens | Mean | (Kirn, |of Kirn, | Mean | (Kirn, |of Kirn, |(Kirn, |et al.)|et al. | (Kirn, |et al.)|et al. |et al.|recalcu- |included |et al. |recalcu- |included | 1949) | lated |their |in 1949) | lated |in their | | by us |diagnosis | | by us |diagnosis -----------------+--------+---------+----------+---------+---------+--------- Ventrals--females|125.67 | 125.71 | 69.4 | 130.07 | 130.07 | 79.6 Ventrals--males |115.97 | 116.61 | 70.0 | 121.22 | 120.87 | 69.7 | | | | | | Caudals--females | 40.99 | 40.82 | 62.8 | 46.79 | 43.82 | 77.4 Caudals--males | 47.75 | 48.29 | 78.3 | 51.67 | 50.29 | 51.0 | | | | | | Tail L./total L. | | | | | | females | .1976| .1976| 69.0 | .2084| .2076| 74.2 Tail L./total L. | | | | | | males | .2336| .2362| 56.1 | .2477| .2423| 79.6 -----------------------------------------------------------------------------

The data presented by Kirn et al. do not demonstrate intergradation between two populations. Moreover, the diagnostic ranges of the number of subcaudals in males of hallowelli and the ratio of tail length to total length in males of gracilis do not include the recalculated means for those characteristics. Furthermore, the means for the following characteristics are dangerously close to being excluded from their respective "diagnostic" ranges: in hallowelli, the number of ventrals in males; in gracilis, the number of subcaudals in females, and the ratio of tail length to total length in females. It is incongruous that Kirn et al. state (p. 243) that "the coefficient of geographic divergence is .6 per degree latitude" for ventrals, and on the same page they state that "The average number of ventrals gradually increases toward the north in Tantilla gracilis except in southern Oklahoma and central Arkansas (the area of intergradation between T. g. gracilis and T. g. hallowelli) where the change seems to be more abrupt." The data presented in Kirn et al. (1949) do not demonstrate an abrupt change.

The present sample of T. gracilis from Kansas is clearly within the geographic range of T. g. hallowelli as mapped by Kirn et al. (1949:241). However, for the sample from Kansas, the mean number of subcaudals of males is well within the diagnostic range for T. g. gracilis (Table 6), the mean number of subcaudals of females is closer to the mean of gracilis than it is to the mean of hallowelli (Table 5), and the mean of the ratio of tail length to total length of both sexes is within or very close to the diagnostic range for gracilis (Table 6).

TABLE 6. Comparison of the Means of Some Characteristics of the Sample of Tantilla gracilis from Kansas (Our Data) with Some of the Diagnostic Characteristics (Kirn et al., 1949:240) of Tantilla gracilis gracilis.