DISTINCTIVE CHARACTERS OF THE CRAYFISH, 233 



Spine. The elevation itself ma}^ be distinguished as the 



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



marked by a longitudinal depression or groove. The 



ABC 



Pig. 61.— A, D, & G,Astac)is torrentlum ; B, E, & H, .1. noljilis; C, F, & 

 I, A. nigresccns (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 and spines ; c, branchio-cardiac grooves 

 inclosing the areola. 



