342 DISTRIBUTION AND ETIOLOGY OF THE CRAYFISHES. 



and left their remains in the mud of the ancient sea 

 bottom. 



Eryma is the onlj' crustacean, which can be certainly 

 ascribed to the Astacomorpha, that has hitherto been 

 found in the strata from the Middle Lias to the litho- 

 graphic slates ; -which last lie in the upper part of the 

 Jurassic series. In the freshwater beds of the Wealden, 

 E.0 Astacomorpha are known, and although no very great 



Pig. 81. — IToploparia longimana (f nat. size). — cp, carapace; 

 r, rostrum, T, telson ; xv., xvi., first and second abdominal somites •. 

 10, forceps ; 20, last abdominal appendage. 



weight is to be attached to a negfttive fact of this kind, it 

 is, so far, evidence that the Astacomorpha had not yet 

 taken to freshwater life. In the marine deposits of the 

 Cretaceous epoch, however, astacomorphous forms, which 



