250 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



are susceptible of being grouped into six genera Asia- 

 coides (fig. 65), Astacopsis, Champs, Pamstacus (fig. 64), 



FIG. <M.Parastacus Irasiliensis (\ nat. size). From southern Brazil. 



Engceus, and Paranephrops on the same principle as 

 that which has led to the grouping of the Northern forms 

 into two genera. But ths same convenience which has 



