. Bulletin. Natural history; Natural history. 234 Illinois Natural History Survey Bulletin Vol. 28, Art. 1 Eutaenia <vagrans nee Baird & Girard, Davis & Rice 1883/':39 (part). Euta'tnia I'agrans nee Baird & Girard, H. Gar- man 1892:268. Tliiimnophis, Blaufuss 1943:56. Tliamnophis ordinatus, Mertens 1951:13. Diagnosis.—A medium-sized snake, a subspecies (largest Illinois specimen 905 mm.) of Tliamnophis sirtalis, differing from T. s. sirtalis only in markings; lateral stripes on anterior part of body interrupted at regular intervals by black crossbars, which are formed by fusion
. Bulletin. Natural history; Natural history. 234 Illinois Natural History Survey Bulletin Vol. 28, Art. 1 Eutaenia <vagrans nee Baird & Girard, Davis & Rice 1883/':39 (part). Euta'tnia I'agrans nee Baird & Girard, H. Gar- man 1892:268. Tliiimnophis, Blaufuss 1943:56. Tliamnophis ordinatus, Mertens 1951:13. Diagnosis.—A medium-sized snake, a subspecies (largest Illinois specimen 905 mm.) of Tliamnophis sirtalis, differing from T. s. sirtalis only in markings; lateral stripes on anterior part of body interrupted at regular intervals by black crossbars, which are formed by fusion of the black spots just above and just below the lateral stripe on each side of body, fig. 220. Variation.—Sexual and ontogenetic vari- ation are apparently identical in T. s. sir- talis and semifaseiata and are described in the account of T. s. sirtalis. Geographic variation in the Chicago gar- ter snake consists of a clinal reduction to- ward the west and south in the frequency of snakes with black crossbars. In northwest- ern Illinois the area in which typical sirtalis replaces typical semifaseiata is probably no more than 40 miles in width. In central Illi- nois the area of intergradation is as much as 100 miles wide. Crossbars in 118 speci- mens of semifaseiata and 45 intergrades have been arbitrarily classified in table 70. Fig. 220.—An adult Thamnophis sirtalis semifaseiata from Lake County, Illinois. The groundcolor is brown on which are superimposed black markings and three longitudinal tan stripes. Table 70.—Geographic variation in crossbarred pattern in Illinois Thamnophis sirtalis semifaseiata and T. s. sirtalis X semifaseiata intergrades, expressed in per cent. Figures in parentheses are numbers of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Illinois. Natural History Surv
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