250 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



are susceptible of being grouped into six genera — Asta- 

 coides (fig. 65), Astacopsis, Cheer aps, Farastacns (fig. 64), 



Fig. QA.—Parasiacus hrasiUensis (| nat. size). From southern Brazil. 



Engceus, and Parancphrnps — on the same princij^le as 

 that which has led to the grouping of the Northern forms 

 into two genera. But the same convenience which has 



