250 THK COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



are susceptible of being grouped into six genera — Asta- 

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



Fis. 64. — Parasiacns Irasiliensis (J nat. size). From southern Brazil. 



Eiigceus, 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 



