THE GENEALOGY OF THE CRAYFISHES. 



345 



Successive Forms of the Astacomorphous Type. 



I. Recent. 



Potariwbiidce. 



Homnrina. 



n. Later Tertiary (^^'«^«J 



III. Earlier Tertiar\-. 



Hoploparia. 



:v. Cretaceous. Astacus. Pseiulastacus. Enoplodytia. Hoploparia. 



\ / 



V. WealJeu 



(Fresh Water). 



VI. Jurassic. 



VII. Liassic. 



/ 



Pscndastaats Eryina. 



JEnjma. 



PeniTus. 



Penceus. 



Penams. 



VIII. Triassio. 



IX. Permian. 



X. Carljoniferous. 



Anthrapaliemori 



XI. Devonian. 



XT'. Silurian. 



XIII. Cambrian. 



If an Astacomorphous crustacean, having characters 

 intermediate between those of Eri/ma and those of 

 Pscudastacits, existed in the Triassic epoch or earHer ; 

 if it gradually diverged into Pseudastacine and Erymoid 

 forms; if these again took on Astacine and Homarine 



