312 DISTRIBUTION AND AETIOLOGY OF THE CRAYFISHES. 



sternum is elevated into a transverse prominence, on the 

 posterior face of which 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 West American Astaci, 

 and approach the Cambari of Eastern North America. 



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

 pairs of lego in the male are provided with similar 



Fra. 78. Cambarus (Guatemala) penultimate leg. cap, coxopodite ; 

 cx.s, coxopoditic setas ; pdb, podobranchia ; bp, basipodite ; ip, ischiopo 

 dite ; mp t meropodite ; cp carpopodite ; pp, propodite ; dp, dactylopodite. 



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

 cation of the penultimate 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 Cambari, the pleurobraiichise appear to be 

 entirely 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. 



