342 DISTRIBUTION AND ETIOLOGY OF THE CRAYFISHES. 



and left their remains in the mud of the ancient sea 

 bottom. 



Eri/ma is the onh' 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, 

 no Astacomorj)]ia are known, and although no verj^ great 



Fig. 81. — TloplojJarla long'xmana (f nat. size). — cp, carapace; 

 ?% rostrum, T, telson ; xv., xvi., first and second abdominal somites ". 

 10, forceps ; 20, last abdominal appendage. 



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

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

 taken to freshwater life. In the marine deposits of the 

 Cretaceous epoch, however, astacomorphous forms, which 



