250 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



are susceptible of being grouped into six genera — Astd- 

 coides (fig. 65), Astacopsis, Chceraps, Parasiticus (fig. 64), 



Fig. 64.— Parantacm trasiliensw (J nat. size). From southern Brazil. 



Engaus, and Paranephrops — on the same principle as 

 that which has led to the grouping of the Northern forms 

 into two genera. But the same convenience which has 



