little_ax, my opinion is if you live in an area with both species, it's going to be tough to tell, especially if the antler is small to medium sized. Large Mule deer will grow antlers that may be somewhat bigger than a large Blacktail, but if I found a really BIG shed, I would assume it came from a Muley unless I had actually seen the buck and knew it to be a blacktail. Supposedly, a mule deer is actually a cross breed between a blacktail and a whitetail - hense the name "mule" (I'm sure alot of us thought it was named for the big ears). Like I said in an earlier post, Blacktail sheds should be darker, and Muley sheds should be lighter, but if they live in the same habitats, they're probably all similar color. Sorry I couldn't be more help. Maybe you could post a picture of the antler in question.