You got it Apparition. I've found that once you can find out how to id both acuminatus and diphreutes, you'll realize that they come in on a 50/50 chance. Distributors don't give a crap, so they just call them the same thing. I've even got in a very rare type of heniochus that came in as "acuminatus," but it was a coral eater type. Just look at the anal fin, if it looks squarish or pointed then it is desphreutus, if it is circular or rounded, then it is acuminatus. That's how I id the both of them. It's the easiest way how, from what I read.
Shoots