Keeled Skimmer, I THINK!

Keeled Skimmer, I THINK!

Observation - Keeled Skimmer, I THINK!. Description: I'm pretty sure that this is a male Kelled Skimmer - it has the pruinose abdomen, bluish eyes and yellow pterostigma. I'm curious about the abdomen tip, though, which shows a very clearly delineated black S10 on this specimen. My book (Dijkstra/Lewingt

I'm pretty sure that this is a male Kelled Skimmer - it has the pruinose abdomen, bluish eyes and yellow pterostigma.

I'm curious about the abdomen tip, though, which shows a very clearly delineated black S10 on this specimen. My book (Dijkstra/Lewington) says "no black tip to abdomen" but here is one. Is this unusual? Am I wrong/missing something?