THE GENEALOGY OF THE CRAYFISHES. 



345 



SUCCESSIVE FORMS OP THE ASTACOMORPHOUS TYPE. 



i Recent Potamobiidce. Homarina. 



Penccut. 



If an Astacomorphous crustacean, having characters 

 intermediate between those of Eryma and those of 

 Pseudastacus, existed in the Triassic epoch or earlier; 

 if it gradually diverged into Pseudastacine and Erymoid 

 forms; if these again took on Astacine and Homarine 



