. Bulletin. Natural history; Natural history. 408 Illinois Natural History Survey Bulletin Vol. 33, Art. 4 cervical spines; suborbital margin smooth. Areola wide, narrowest part about 19-25 percent of length. Chelae large, heavily punctate; palm with 2-3 rows of tubercles on mesial margin. Form I gonopod terminates in two short, straight elements: a sclerotized central projection and an unsclerotized mesial process. Dorsally green to red brown; fingers of chelae with red tips, subdistal black bands. Fitzpatrick (1967) found O. propin- cjiius to be the most variable species among the Propinquus
. Bulletin. Natural history; Natural history. 408 Illinois Natural History Survey Bulletin Vol. 33, Art. 4 cervical spines; suborbital margin smooth. Areola wide, narrowest part about 19-25 percent of length. Chelae large, heavily punctate; palm with 2-3 rows of tubercles on mesial margin. Form I gonopod terminates in two short, straight elements: a sclerotized central projection and an unsclerotized mesial process. Dorsally green to red brown; fingers of chelae with red tips, subdistal black bands. Fitzpatrick (1967) found O. propin- cjiius to be the most variable species among the Propinquus group of spe- cies but also to lack taxonomically recognizable subspecies. "O. wmaen- sis," previously thought to be a para- patric relative of O. propinquus oc- cupying areas of Iowa adjacent to Il- linois (Fitzpatrick 1968), has been rele- gated to the synonymy of O. propin- quus by Page (1985). Distribution and Habitat.—O. pro- pinquus ranges from southern Ontario and Quebec south to Illinois, Indiana, Ohio, northern Pennsylvania, New York, and Massachusetts. To the west, its range extends into eastern Iowa and southeastern Minnesota (Fig. 142). In Illinois, O. propinquus occurs in Lake Michigan and in the Wabash. Il- linois, Rock, Mississippi, and extreme upper Kaskaskia drainages (Fig. 143). In the Wabash drainage, it extends as far south as White County, is wide- spread in the Embarras River, but is absent in the Little Wabash River sys- tem. In the Illinois and Mississippi rivers, it occurs as far south as Calhoun and Rock Island counties, respectively. Throughout its range in Illinois, O. propinquus is the most common crayfish in clean rocky riffles (Fig. 144). In the fast, rubble and gravel riffles characteristic of the Vermilion, Kan- kakee, and upjH'r Rock drainagis, O. propinquus often is abundant. Its ab- sence in most of western and central Illinois presumably is due to the ab- sence of suitable habitat; its absence in southern Illinois apparently is
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