392 



NORTH AMERICAN INDEX FOSSILS. 



surface strongly denticulate; length of propodite nearly twice the 

 width; length of carpus similar, width a little greater. 

 Abundant in nodules of Astoria shales of Oregon. 



XX. AsTACus Fabricius. 



Body cylindroidal ; cephalothorax with strong neck furrow ; 



rostrum triangular, narrow; inner antennae with short shaft, and 



short double flagella; outer antennae with longer shaft, and long 



flagella, with pronounced scale ; sternum narrow ; last thoracic seg- 



FiG. 1694. Cancer antennarins Stimpson (male). A recent species from the 

 California coast. Distinguished by its long outer antennae and its hairiness, X %• 

 The regions of the cephalothorax are faintly outlined. (After Stimpson, Bost. Soc. 

 Nat. Hist. Proc, VI.) 



ment not fused with the preceding; three anterior thoracic legs 

 chelate, the first one very large, with dactylus on the inside, whereas 

 in the other two it is on the outside. 



The fresh water crayfish of America include the genera Cam- 

 harus and Astacus {^= P otamohius according to Ortmann). The 

 distinction between the two genera lies in the character of the 



