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 fol
lowing 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.
| Characteristics | T. g. gracilis | T. g. hallowelli | ||||
|---|---|---|---|---|---|---|
| Mean (Kirn, et al. 1949) | Mean (Kirn, et al.) recalculated by us | Per cent specimens of Kirn, et al. included their diagnosis | Mean (Kirn, et al. in 1949) | Mean (Kirn, et al.) recalculated by us | Per cent specimens of Kirn, et al. included in their 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). How
ever, 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.
| Characteristic | Diagnostic range for T. g. gracilis | Mean of the sample ("T. g. hallowelli") from Kansas |
|---|---|---|
| No. of subcaudals males | 40-50 | 48.4 (N = 109) |
| Tail L./ Total L. females | .160-.200 | .20 (N = 79) |
| Tail L./ Total L. males | .200-.235 | .23 (N = 109) |
Smith and Sanders (1952:218) pointed out an error in the range of subcaudals in female T. g. gracilis as stated in table 1 (p. 247) of Kirn et al. We
add some additional corrections that should be made on the same page. In table two, column two ("Sex"), the words "male" and "female" are reversed for each characteristic. Also, in table two, column four ("Means from data of Force"), the means for caudals should be corrected from 33.61 to 43.61 in females and from 39.99 to 50.32 in males, as based on our recalculations from Force's data; we did not recalculate the means of Force's data for the other characteristics.
The discussion above demonstrates that the number of subcaudals and the ratio of tail length to total length are weak characteristics for diagnosing T. g. gracilis and T. g. hallowelli. The only remaining diagnostic characteristic given by Kirn et al. (1949) is the number of ventrals. Nevertheless, a step-cline in the number of ventrals, if one exists, is yet to be demonstrated. Therefore, we completely agree with Dowling (1957:32), who stated that "... the overlap in each character is so great that any subspecific differences appear to be as yet undefined. It is here suggested that T. gracilis be retained as binomial...."
LITERATURE CITED
Baird, S. F. and Girard, C.
1853. Catalogue of North American Reptiles in the museum of the Smithsonian Institution. Part I.—Serpents. Smithsonian Misc. Colls., 2:1-172.
Blanchard, F. N.
1938. Snakes of the genus Tantilla in the United States. Zool. Ser. Field Mus. Nat. Hist., 20(28):369-376.
Conant, R.
1958. A field guide to reptiles and amphibians. Houghton Mifflin Co., Boston, 366 pp.
Cope, E. D.
1900. The crocodilians, lizards, and snakes of North America. U. S. Nat. Mus. Rept. (1898), 153-1270.
Dowling, H. G.
1951. A proposed standard system of counting ventrals in snakes. British J. Herpetology, 1(5):97-99.
1957. A review of the amphibians and reptiles of Arkansas. Occas. Paps. Univ. Arkansas Mus., No. 3:1-51.
Dunn, E. R.
1928. A tentative key and arrangement of the American genera of Colubridae. Bull. Antivenin Inst. Amer., 2 (147):18-24.
Force, E. R.
1935. A local study of the opisthoglyph snake Tantilla gracilis Baird and Girard. Papers Michigan Acad. Sci., Arts and Letters, 20:645-659.
Kirn, A. J., Burger, W. L., and Smith, H. M.
1949. The subspecies of Tantilla gracilis. Amer. Midl. Nat., 42(1):238-251.
Peters, J. A.
1960. The snakes of the subfamily Dipsadinae. Misc. Pubis. Mus. Zool., Univ. Michigan, No. 114:1-224.
1964. Dictionary of herpetology. Hafner Publ. Co., New York, 392 pp.
Schmidt, K. P. and Davis, D. D.
1941. Field book of snakes. G. P. Putnam's Sons, New York, 365 pp.
Smith, H. M. and Sanders, O.
1952. Distributional data on Texan amphibians and reptiles. Texas J. Sci., 4(2):204-219.
Taylor, E. H.
1936. Notes and comments on certain American and Mexican snakes of the genus Tantilla, with descriptions of new species. Trans. Kansas Acad. Sci., 39:335-348.
Wright, A. H. and Wright, A. A.
1957. Handbook of snakes. Comstock Publ. Assoc, Cornell, Vol. II, pp. 565-1105.
Department of Biology, The University of New Mexico, Albuquerque, 87106, and Department of Zoology, The University of Arizona, Tucson, 85721.
Transmitted July 11, 1967.
Textual representation of complete dorsal scale formula on [page 622].
| 15 | 6 + 7(2) | 13 | + 7(4) | 14 | 15 | 6 + 7(11) | 13 | , | ||
| 6 + 7(2) | +7(5) | 6 + 7(11) | 6 = 6 + 7(17) | |||||||
| 14 | 13 | , | ||||||||
| 6 + 7(18) | +7(25) | |||||||||
| 14 | + 7(26) | 15 | 14 | 6 + 7(38) | 13 | +7(39) | 14 | , | ||
| 6 + 7(36) | +7(42) | |||||||||
| 15 | 14 | , | ||||||||
| -6(45) | +7(53) | |||||||||
| 15 | 7 + 8(67) | 14 | + 7(69) | 15 | 14 | 15 | , | |||
| 6 + 7(90) | +7(93) | 6 + 7(99) | ||||||||
| 14 | 15(122). | |||||||||
| + 7(100) | ||||||||||