HIGHER CRUSTACEANS (MALACOSTRACA) 



847 



36 (35) Male copula tory 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 obliterated in the middle. Chelae short and broad. 



Section of Cambarus gracilis Bundy 1876. 



Three species, burrowing forms, on the coastal plain from South Carolina to Texas, and 

 northwards over the prairie region to Wisconsin. 



