DISTINCTIVE CHARACTERS OF THE CRAYFISH. 233 



spine. The elevation itself maj^ be distinguished as the 



liost-orhital ridge. The flattened surface of this ridge is 



marked b}^ a longitudhial depression or groove. The 



A B C 



Fig. 61.— a, D, & G,Astacvs torrcntUim ; B, E, & H, .1. fwbilis; C, F, & 

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

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

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

 inclosing the areola. 



