16 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



(Hagen, 1870, p. 21) affecting principally the first pair of pleopods, 

 the hooks on the ischiopodites of the third pereiopods, and the cheli- 

 peds. In the breeding males, "Form I," the first pleopod has one 

 corneous terminal element, and the hook of the ischiopodite of the 

 third pereiopod is developed more strongly and usually more acutely; 

 the cheliped is usually more robust and frequently the crayfish is more 

 vividly colored (ignoring the fact that all freshly molted crayfishes 

 are more brightly colored than at any other time.) The nonbreeding 

 males are designated "Form II." 



The life cycle of Cambarus I. longulus (see Smart, 1962) is better 

 known than that of any of the other species in the area, and it appears 

 that it does not differ, except perhaps in details, from that of C. 

 acuminatus (see Word and Hobbs, 1958, p. 436) and 0. juvenilis. The 

 young of C. I. longulus hatch from the egg in early spring, undergo a 

 series of molts through the summer and fall but cease to grow through- 

 out the winter. The following spring, growth resumes and in Septem- 

 ber juvenile males molt to the breeding stage (Form I). The first 

 breeding season extends from late fall to spring when the male molts 

 to the nonbreeding stage (Form II). In September it again molts 

 to the first form and passes its second breeding season, molting to 

 the second form in the spring. Most of the males die after the second 

 breeding season but a few undergo one additional molt to the first 

 form in the fall and die in the spring. Females carry their eggs during 

 the late winter and early spring; however, an occasional female will 

 be found in midsummer with a full complement of eggs on the pleopods. 

 It is obvious, on the basis of this brief account, that first form males 

 of C. 1. longulus, C. acuminatus, and 0. juvenilis are abundant in the 

 late fall, winter, and early spring but are rare at other seasons. 



In contrast, first form males of C. sciotensis, C. b. bartonii, and C. 

 carolinus may be collected at almost any time during the year, and 

 females with eggs occur, for the most part, during the summer and 

 fall months. Almost no life history data are available for C. carolinus 

 and C. sciotensis. 



Additional data for all of the crayfishes treated here may be found 

 in the indispensable contributions of Ortmann (1905, 1931). 



Key to Cravfishes 



1 Rostrum with marginal spines; first pleopod of male terminating in two 

 straight rami Orconectes juvenilis 



1' Rostrum without marginal spines; first pleopod of male terminating in 

 two short rami that are recurved at angles of approximately 90°. 



Cambarus . . 2 



