THE GENEALOGY OF THE CRAYFISHES. 



345 



Successive Forms of the Astacomorphous Type. 



sent. FotamobiidcB. Homarlna. 



n. Later Tertiary £*£» 



in. Earlier Tertiary. 



Hoploparia. 



iv. Cretaceous. Astacus. Pseudastacus. Enoplodytia. Hoploparia. 



v. Wealden 



(Fresh Water). 



vi. Jurassic. 



vii. Liassic. 



Pseudastacus Eryma. 



JSryma. 



Penceus. 

 Penceus, 



viii. Triassic. 



x. Carboniferous. 



Anthrapalmmon 



xi. Devonian. 



xir. Silurian. 



xiii. Cambrian. 



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 

 16 



