342 DISTRIBUTION AND ETIOLOGY OF THE CRAYFISHES. 



and left their remains in the mud of the ancient sea 

 bottom. 



Eryma 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 Astacomorpha are known, and although no very great 



Fig. 81. — IIoplojMria Umginiana (| nat. size). — cj)^ 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 negative fact of this kind, it 

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

 taken to freshwater life. In the marine deposits of the 

 Cretaceous epoch, however, astacomorphous forms, which 



