250 THE COMPARATIVE MORPHOLOGY OF THE CRAYFISH. 



are susceptible of being grouped into six genera — Asta- 

 coides (fig. G5), Astacops^is, Chferops, Parastacvs (fig. 64), 



Fig. Qi. — I'ara.iiacus hvaisilicnsis (\ nat. size). From southern Brazil. 



E)tgaxis, and Parancphrops — 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 



