. Bulletin. Natural history; Natural history. November, 1961 Smith : Amphibians and Reptiles of Illinois 157. Fig. 139.—A subadult Trionyx spinifer spinifer from Tazewell County, Illinois. The shell and body are tan or brown above, white below. The juvenile is paler than the adult, and the carapace markings and the mottling of soft parts are more prominent. Both pro- portionate width and height of the shell de- crease as the turtle becomes adult. Since the male is intermediate in size between the juvenile and the adult female, changes in shell ratios can be illustrated by comparing the
. Bulletin. Natural history; Natural history. November, 1961 Smith : Amphibians and Reptiles of Illinois 157. Fig. 139.—A subadult Trionyx spinifer spinifer from Tazewell County, Illinois. The shell and body are tan or brown above, white below. The juvenile is paler than the adult, and the carapace markings and the mottling of soft parts are more prominent. Both pro- portionate width and height of the shell de- crease as the turtle becomes adult. Since the male is intermediate in size between the juvenile and the adult female, changes in shell ratios can be illustrated by comparing the of carapace width to length and carapace height to length ratios of juveniles, males, and females, table 42. Geographic variation in the eastern spiny softshell within Illinois is manifested by an east-to-west reduction in the size of the cen- tral ocelli of the carapace. This clinal vari- ation represents intergradation of eastern spinifer with hartivegi, which occurs west of the Mississippi River. In eastern Illinois the ocelli of spinifer are typically large in the center of the carapace; they decrease in size toward the periphery of the shell. In western Illinois occasional specimens have enlarged central ocelli, but the majority tend to have less difference in size between central and peripheral ocelli. These charac- ters are difficult to measure and, since no north-to-south variation has been discerned, the patterns of the available material have been assigned to "hartwegi-\\\it,^^ "interme- diate," or "spinifer-Wkt^ groups and di- vided into a western Illinois sample and an eastern Illinois sample, table 43. The data shown in table 43 are essen- tially in agreement with the findings of Co- nant & Goin (1948), who described hart- luegi, except that our samples suggest that Table 42.—Ontogenetic variation in carapace ratios of Illinois Trionyx spinifer. Figures in parentheses are numbers of specimens. Adults Characteristic JUVENII ES ^IW Males (
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