. Bulletin. Natural history; Natural history. Fig. 121. immunis. -Total distribution of Orconectes spines; suborbital margin bluntly an- gular. Areola narrow, constricted an- teriorly, narrowest part about 10 percent of length. Chelae moderate in size, heavily punctate; palm with 2-3 rows of small tubercles on dorsomesial mar- gin. Form I gonopod terminates in two fairly short (central projection about 23 percent of total length of gonopod) elements curved at 90° angle to main axis: a sclerotized central projection and an unsclerotized mesial process. Annulus ventralis distinctive, with fos- s
. Bulletin. Natural history; Natural history. Fig. 121. immunis. -Total distribution of Orconectes spines; suborbital margin bluntly an- gular. Areola narrow, constricted an- teriorly, narrowest part about 10 percent of length. Chelae moderate in size, heavily punctate; palm with 2-3 rows of small tubercles on dorsomesial mar- gin. Form I gonopod terminates in two fairly short (central projection about 23 percent of total length of gonopod) elements curved at 90° angle to main axis: a sclerotized central projection and an unsclerotized mesial process. Annulus ventralis distinctive, with fos- sa far to one side. Dorsal color highly variable, from uniformly red brown to light green with dark brown mottling; fingers of chelae without bright red tips and subdistal black bands. O. immunis is a member of the J'irilis group of Orconectes and is most similar to O. alabamensis, O. rhoadesi, and O. validits. spec ies inhabiting the Caim- berland, Tennessee, and Mobile Bay drainages. Some populations of the wide-ranging O. immunis have been considered sufficiently distinct to war- rant laxonomic recognition (see syn- onymy abo\e), and Bovbjerg (1952) referred to northeastern Illinois popu- lations as "O. immunis x ; However, Williams &: Leonard (1952) found that the characteristics which had been used to distinguish subspecies varied clinally and could not be used to diagnose geographically limited popu- lations. No subspecies were recognized by Hobbs (1974b). Distribution and Habitat.—O. im- munis ranges from southern Quebec, Maine, and Connecticut west through the Great Lakes (except Lake Superior), to eastern Wyoming and eastern Col- orado (Fig. 121). The southern edge of the range approximates the southern limit of Pleistocene glaciation but extends farther south into western Ken- tucky and Tennessee and farther west into the Great Plains. An isolated pop- ulation in Muddy Creek (Canadian- Arkansas River drainage), Okfuskee. Fig. 122.—Distributi
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