DISTINCTIVE CHARACTERS OF THE CRAYFISH. 



233 



spine. The elevation itself ma}^ be distiiiguislied as the 



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



marked h}' a longitudinal depression or groove. The 



ABC 



Fig. 61.— A, D, & G,Astactis torrcntium ; B, E, & H, ^l. noMlis; C, F, & 

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

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

 a, h, post-orbital ridge aiid spines ; c, branchio -cardiac grooves 

 inclosing the areola. 



