University of Kansas Publications
Museum of Natural History

Volume 17, No. 15, pp. 613-629, 6 figs.
May 14, 1968

Morphological Variation in a Population of the Snake, Tantilla gracilis Baird and Girard

BY

LAURENCE M. HARDY AND CHARLES J. COLE

University of Kansas
Lawrence
1968

University of Kansas Publications, Museum of Natural History

Editors: E. Raymond Hall, Chairman, Frank B. Cross, Henry S. Fitch, J. Knox Jones, Jr.

Volume 17, No. 15, pp. 613-629, 6 figs.
Published May 14, 1968

University of Kansas
Lawrence, Kansas

PRINTED BY
ROBERT R. (BOB) SANDERS, STATE PRINTER
TOPEKA, KANSAS
1968

31-9422

Morphological Variation in a Population of the Snake, Tantilla gracilis Baird and Girard

By

LAURENCE M. HARDY AND CHARLES J. COLE

INTRODUCTION

Variation of selected taxonomic characteristics of flat-headed snakes (Tantilla gracilis Baird and Girard) from several midwestern states was studied by Force (1935), but she did not attempt a comprehensive evaluation. Taylor (1936) reported on variation in T. gracilis from various localities in Kansas; Kirn, Burger, and Smith (1949) studied selected structures of specimens of T. gracilis from throughout its range. The present study was undertaken to determine the variation in both currently used and potential taxonomic characteristics of T. gracilis from one locality.

We are thankful to Charles W. Myers, Gorgas Memorial Laboratory, for suggestions concerning characteristics examined. We are indebted to Drs. William G. Degenhardt, University of New Mexico, Herndon G. Dowling, New York Zoological Society, Charles H. Lowe, University of Arizona, and Richard G. Zweifel, American Museum of Natural History, for criticizing the manuscript. Dr. William E. Duellman permitted us to study specimens in the University of Kansas Museum of Natural History.

Materials and Methods

The specimens examined were donated to the Museum of Natural History, University of Kansas, by the late Paul Anderson of Independence, Missouri. All specimens (KU numbers 83435-83680; N = 246) were collected in the vicinity of Winfield, Cowley County, Kansas, by Charles E. Burt and students from Southwestern College in the period from 1938 to 1941, inclusive.

Both authors gathered data on most characteristics and examined each atypical individual. Hardy determined characters of the maxillae (which were removed; N = 20), body and total lengths, and the scale formula of KU 83620.

We examined 22 characteristics of external morphology and 10 of the maxillae. All paired characteristics (excepting those of the maxillae) were examined on both sides of each snake and are referred to from the left side to the right side (for example, "preoculars 1-2" means there is one preocular on the left side and there are two on the right). Oviducts and oviducal eggs were observed on specimens designated as females; hemipenes were examined on specimens designated as males. Total length was measured by straightening each snake along a 300 mm. scale. Tail length was measured only on snakes having complete tails, and body length (snout-vent) was considered as total length minus tail length. The body length was measured on snakes having incomplete tails.

Supralabials, infralabials, preoculars and postoculars were counted, and we followed Peters (1960:9) in determining the nature of the temporals. Occasionally the primary (anterior) temporal is separated from the postocular by contact of the parietal and a supralabial (Taylor, 1936:338). We followed Peters (1964:219-220) in determining characteristics of the nasal and we looked for contact of the prefrontal with particular supralabials (Taylor, 1936:338). We determined which supralabials are in contact with the eye and whether the mental is in contact with the anterior pair of chin-shields.

The number of rows of dorsal scales was determined at five locations: a) around the neck—counts were made from each side diagonally and posteriorly from the anteriormost dorsal scale in contact with the first ventral (see below)—counts from the left and right sides are the first and second counts, respectively, recorded in the scale formula; b) one head length posterior to head—counts were made either diagonally and posteriorly or in a zig-zag pattern, beginning at the end of the second count around the neck—this is the third count recorded in the scale formula; c) midbody (approximated)—counts were made either diagonally and posteriorly or in a zig-zag pattern—this is the fourth count in the scale formula; d) anterior to anus (preanal)—counts were made in a zig-zag pattern beginning on one side and ending on the other at the first dorsal scale in contact with the anal plate—this is the fifth count in the scale formula.

We followed the method of Dowling (1951:98-99) in counting ventrals, and the anal plate was determined as entire, divided, or partly divided. Subcaudals were counted on only the right side beginning at the first scale that contacts a corresponding scale from the opposite side; fusion of particular pairs of subcaudals was determined. The "spine" at the tip of the tail was not counted. The head scutellation of each specimen was examined for abnormalities.

We determined the number of fangs and the number of maxillary teeth anterior to them and recorded the presence or absence of a diastema between the anterior fang and the maxillary tooth immediately preceding it. The diastema, if present, is a space distinctly wider than the spaces separating the prediastemal teeth.

The point of intersection of two perpendicular lines of an ocular grid determined which tooth-socket occurs directly opposite the distal tip of the suborbital process (Fig. 5b), but if that point occurs between two sockets then the number recorded was the number of the tooth immediately anterior to that point