(Hey, Nick -- I thought we had settled this one years ago :-) )

Since both Lancet and Dusky have harpoon cerci, let me play devil's advocate... How do we account for the prominent side tooth on the cerci (top view)? Assuming it's not a photo artifact, do Lancets ever show prominent teeth on the side of the cerci? And what about the very weak club flanges? Shouldn't they be more pronounced in a male Lancet?

The club shape is pretty similar between the two. I've never seen a Dusky without a prominent ventral tooth on the cerci. I wouldn't say that Dusky has the classic tapering harpoon shape that Lancet has. The lack of the taper is what produces the tooth instead of an arrowhead-like shape that Lancet has. I have seen Lancets that appear to have a bit of a tooth on the outside of the cerci. That tooth should be even more prominent on a Dusky, IMO.

I'm happy to be wrong on this. FWIW, I've never seen so much yellow at the tip of a Dusky, either, but I know that's not a reliable field mark.

Okay, I definitely see that the shape of the ventral tooth is smoothly tapered, just as in Paulson's Lancet illustration (p. 267). But Paulson's Lancet cerci top view shows a cerci side edge that is very smoothly rounded ("convex" for lack of a better word). Paulson's Dusky cerci top view shows a side edge with two "concave" edges on either side of the prominent tooth. In my last two close-ups (top view) I see the same shape, which I traced in blue in Photoshop. It looks at least as prominent as Paulson's illustration. In the "lightly-side-toothed Lancets" you've seen, did the cerci side edges still have a more or less "smoothly concave" profile or did they approach the "double concave" profile like a Dusky?

Now I'm second-guessing myself! This lateral view of the cerci just does not look like a Dusky to me, but I could be convinced that it's an odd angle or something. There are no good photos of Lancet cerci from the same angle in BugGuide. I'll catch some of each species this week and try to post comparison photos.

Just to remind you, back in 2014 (on that other web site) you said this about the same images:

"Wow, that is the yellowest Dusky Clubtail I've ever seen! I would not have hesitated to call this a Lancet in the field."

Apparently I convinced you then, but obviously it didn't take. ;-)

I don't remember this bug at all! Sigh. I hate my memory sometimes. Was this on iNat?

It was on ILbirds.

Funny, I never forgot this one :-)

Ha, okay then!

Incidentally, I only stumbled back on this bug because I was looking for yellow Dusky examples! I had one today that was the yellowest I've seen in person: http://www.inaturalist.org/observations/6565302

Ugh, okay, I've convinced myself this is just an odd angle on the cerci that is making the tooth not stand out. Sorry, Mark!