. Bulletin. Natural history; Natural history. 272 Illinois Natural History Survey Bulletin Vol. 28, Art. 1 Table 91.—Geographic variation in Illinois Crotalus horridus. Figures in parentheses are numbers of specimens. Number of Scale Rows at MiD-BoDV Perry Counties (12) With 21 rows (per cent of speci- mens) With 23 rows (per cent of speci- mens) With 24 rows (per cent of speci- mens) With 25 rows (per cent of speci- mens) 0 33 25 42 Monroe-Pike Counties (8) Rock Island- Jo Daviess Counties (5) 0 76 12 12 Coles-Jasper Counties (4) 0 80 0 20 25 25 25 25 intergrades. This disposition
. Bulletin. Natural history; Natural history. 272 Illinois Natural History Survey Bulletin Vol. 28, Art. 1 Table 91.—Geographic variation in Illinois Crotalus horridus. Figures in parentheses are numbers of specimens. Number of Scale Rows at MiD-BoDV Perry Counties (12) With 21 rows (per cent of speci- mens) With 23 rows (per cent of speci- mens) With 24 rows (per cent of speci- mens) With 25 rows (per cent of speci- mens) 0 33 25 42 Monroe-Pike Counties (8) Rock Island- Jo Daviess Counties (5) 0 76 12 12 Coles-Jasper Counties (4) 0 80 0 20 25 25 25 25 intergrades. This disposition of Illinois specimens is in complete agreement with the range definition of the two races as pointed out by Gloyd (1940). Other variation in a sample of 30 timber rattlesnakes from various parts of Illinois is apparently individual. There is some evi- dence that snakes in one colony may dififer from those in another colony in minor de- tails of pattern. This variation among colo- nies is not clear-cut and may be fortuitous. Anterior scale rows in the 30 snakes men- tioned above are as follows: 24 in 13 per cent of sample, 25 in 17 per cent, 26 in 50 per cent, and 27 in 20 per cent; posterior scale rows 18 in 3 per cent, 19 in 74 per cent, 20 in 20 per cent, and 21 in 3 per cent. Supralabials are highly variable; they range from 12 to 16 per side; 13 or 14 occur most frequentl5^ Infralabials range from 13 to 18, 14 or 15 occuring most frequently. The number of body bands ranges from 20 to 26, averaging A dark postorbital stripe on each side of the head is present in most snakes; it is dim in occasional specimens, particularly in those from northwestern and eastern Illinois. Light-centered lateral spots on anterior portion of body and black spots or dashes between the bands occur on nearly all the Illinois timber rattlers. The black phase, which occurs in more eastern populations of timber rattlesnakes, has not been encountered in this state, and only one of the Illinois
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