312 DISTRIBUTION AND ATIOLOGY 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 legs in the male are provided with similar 
Fic. 78.— Cambarus (Guatemala) penultimate leg. cxp, coxopodite ; 
ex.s, coxopoditic setze ; pdb, podobranchia ; by, basipodite ; ip, ischiopo- 
dite; mp, meropodite ; cp carpopodite; py, 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 pleurobranchie 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. 
