Could it be new?
I took this shot of a gomphid along the river deep in the Batopilas Canyon on my recent trip to Mexico, it mystified me (admittedly that's not too unusual). It looked like a Stylurus but my reference list of the dragonflies of Chihuahua and Sinaloa (re-worked from one of Dennis Paulson's online publications) listed no species of that genus in the region. When I got back home I sent the image to the very same Dennis Paulson - the North American odo-guru.
Dennis responded "It looks much like Stylurus olivaceus, but there are no records of that species from Mexico. The thoracic pattern is different enough, however, that I hesitate to call it olivaceus, especially as it would be a first record for the country. In addition, and this is probably even more important, the closest record of olivaceus is many hundreds of miles away (far from the US/Mexican border), so the probability of it being that species seems very low. There is a definite possibility of an undescribed species."
Now we just need someone to go and collect one so I can add it to my list! Although it has to be said we had to endure a rather tense roadside interview with some heavily-armed narco-gangsters to get to the site two week ago...