THE GENEALOGY OF THE CRAYFISHES. 



S45 



Successive Foeiis of the Astacomorphous Type. 



I. Recent 



Potamobiidce. 



Homarina. 



Penceus. 



, . m X- A4acus 



II. Later Tertiary ^j^^j^^) 



III. Earlier Tertiary. 



Hoploparia. 



IV. Cretaceous. Astacus. Psevxlastacus. Enoplodytia. Hoploparia. 



/ 



V. Wealfleu 



(Fresh Water). 



VI. Jurassic. 



VII. Liassic. 



Pseudaitacus Eryma. 



Eryma. 



Pencmis. 



Penceus. 



VIII. Triassic. 



IX. Permian. 



X. Carboniferous. 



XI. Devonian. 



XXI. Silurian. 



XIII. Cambrian. 



Anthrapalcemon 



If an Astacomori)hous crustacean, having characters 



intermediate between those of Eryma and those of 



Pseiidastacus, existed in the Triassic epoch or earlier ; 



if it gradually diverged into Pseudastacine and Er3'moid 



forms ; if these again took on Astacine and Homarine 

 16 



