THE GENEALOGY OF THE CRAYFISHES. 



345 



Successive Foems of the Astacomorphous Type. 



I. Kecent. 



PotamobiidcB. 



Homarina. 



Penccus. 



II. Later Tertiary 



Antaeus 

 (Idaho). 



III. Earlier Tertiary, 



IV. Cretaceous 



Hoploparia. 



Asiacus. Psciuladacus. Enoploclytia. Hoploparia. 



"Wealflen 

 (Fresh Water). 



nil. Cambrian. 



If an Astacomorplious 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 



