DISTINCTIVE CHARACTERS OF THE CRAYFISH. 



233 



spine. The elevation itself may be distinguished as the 



post-orbital ridge. The flattened surface of this ridge is 



marked by a longitudinal depression or groove. The 



A BC 



Fig. 61.— A, D, & G,Astacvs torrentinm ; B, E, & H, A. nolilis; C, F, & 

 I, A. nigreseens (nat. size). A— C, Dorsal views of carapace ; D— F, 

 side views of third abdominal somites ; G — I, Dorsal views of telson. 

 a, ft, post-orbital ridge and spines ; c, branchio-cardiac grooves 

 inclosing the areola. 



