250 THE COMPAEATIVE MORPHOLOGY OF THE CRAYFISH. 



are susceptible of being grouped into six genera — Asta- 

 coides (fig. 65), Astacopsis, Chcera})8, Parastacus (fig. 64), 



Fig. 64. — Parasiacus Irasiliensis (^ nat. size). From soutbern Brazil. 



Engaus, and Parancplwops — on the same piinciple as 

 that which has led to the grouping of the Northern forms 

 into two genera. But the same convenience which has 



