THE GENEALOGY OF THE CRAYFISHES. 



345 



Successive Forms of the Astacomorphous Type. 



1. Recent 



Potamobiidoe. 



Homarina. 



II. Later Ternary ^^^.^^^y 



in. Earlier Tertiary. 



Hoploparia. 



IV. Cretaceous. Asiacus. Psciulaitacus. Enoploclytia. Hoploparia. 



V. Wealilen 



(Fresh Water). 



VI. Jurassic. 



VII. Liassio. 



VIII. Triassic. 



IX. Permian. 



X. Carboniferous. 



XI. Devonian. 



XII. Silurian. 



XIII. Cambrian. 



Pseudastacus Eryma. 



Eryma. 



Anthrapalcemon 



Pencmis. 



Penmus. 



Penceus. 



If an Astacomorphous crustacean, having characters 

 intermediate between those of Eryma and those of 

 Pseudastaais, existed in the Triassic epoch or earlier ; 

 if it gradually diverged into Pseudastacine and Erymoid 

 forms ; if these again took on Astacine and Homarine 



