. Fresh-water biology. Freshwater biology. HIGHER CRUSTACEANS (MALACOSTRACA) 847 36 (35) Male copulatory organs more or less complex. Some peraeopods of the male with hooks on the ischiopodite. Female with receptaculum seminis (annulus ventrahs) upon the sternum of the thorax. No pleurobranchiae present. Cambarus Erichson . 37 Restricted to North America east of the Rocky Mountains, Mexico, Guatemala, and Cuba. It contains between seventy and eighty species, which fall into six sub- genera, four of which are represented in the United States. The geographical distribution of the species of Camb

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. Fresh-water biology. Freshwater biology. HIGHER CRUSTACEANS (MALACOSTRACA) 847 36 (35) Male copulatory organs more or less complex. Some peraeopods of the male with hooks on the ischiopodite. Female with receptaculum seminis (annulus ventrahs) upon the sternum of the thorax. No pleurobranchiae present. Cambarus Erichson . 37 Restricted to North America east of the Rocky Mountains, Mexico, Guatemala, and Cuba. It contains between seventy and eighty species, which fall into six sub- genera, four of which are represented in the United States. The geographical distribution of the species of Cambarus is very interesting, and apt to furnish evidence for the geo- logical changes of our river-systems. This genus is also eminently fit for ecological studies on account of the great diversity of the habit-preferences of the single species. Besides the four subgenera treated here, two others have been distinguished (.Para- cambarus and Procambarus), but they do not possess representatives in the United States. Fig. 1314. Cambarus bartoni'Fahnzvii. X I. (After Paulmier.). The most common species in the eastern United States, found in small streams of the Appalachian chain from Tennessee and the Carolinas to Maine and New Brunswick. 37 (44) Sexual organs of male with more than two tips. 38 38 (43) Third, or third and fourth, peraeopods of the male with hooks on the ischiopodite. Sexual organs of male blunt or truncated, with one soft tip, and several short, horny teeth. Subgenus Cambarus Ortmann . 39 Distribution: Chiefly southern and southwestern in the United States. 39 (42) Male with hooks on third peraeopods 40 40 (41) Areola narrow. Chelae elongated. Section of Cambarus simulans Faxon 1884. The areola is the posterior, median dorsal part of the carapace, included between the lines which bound the lateral (branchial) regions. The areola is " obliterated, " when these lines come into contact. Two species in the southwestern United States and Mexico. 41 (40) Areola o