I found this freshwater crayfish carapace on the forest floor. It wasn't in great shape and was missing some of the distinguishing characteristics that I would normally use for identification. The carapace was about 5 cm long.
Spotted on the ground in a mostly coniferous forest - near the edge of a river.
I think it's in the family Cambaridae. It could be Orconectes propinquus, Orconectes rusticus, or Cambarus robustus...But, I'm not sure.