312 DISTKIBIJTION AND ETIOLOGY OF THE CRAYFISHES. 



sternum is elevated into a transverse prominence, on the 

 posterior face of wliicli there is a pit or depression.* 



In both these characters, but more especially in the 

 former, the Amurland and Japanese Astaci depart from 

 both the Pontocaspian and the AVest American Astaci, 

 and approach the Camhari of Eastern North America. 



In these crayfishes, in fact, one or both of the same 

 pairs of legs in the male are provided with similar 



Fig. 78. — Camliarns (Guatemala) penultimate leg. cxjy, coxopodite ; 

 cx.s, coxopoditic setse ; 2^dh, podobranchia ; hp, basipodite ; ?/>, ischiopo- 

 dite ; nij), meropodite ; cj) carpopodite ; 2U^' propodite ; djy, dactylopodite. 



hook-like processes ; while, in the females, the modifi- 

 cation of the 2)eniiltimate thoracic sternum is carried 

 still further and gives rise to the curious structure de- 

 scribed by Dr. Hagen as the *' annulus ventralis." 



In all the Camhari, the pleurobranchiie appear to be 

 entirel}^ suppressed, and the hindermost podobranchia has 

 no lamina ; while the areola is usually extremely narrow. 

 The proportional size of the areola in the Amurland 



* Kessler, 1. c. 



