The photos here are of a mocha emerald (Somatochlora linearis). It’s a dragonfly of the forest, near small shady streams. They seem to be more common near streams which dry up during summer. That habitat does occur here at the museum.
I’ve only encountered mocha emeralds here on two other occasions. The first was in July of 2008 when I found a partially eaten individual on the path in Catch the Wind. I saw a live mocha in June of 2011 on the Dinosaur Trail http://www.natureblog.org/mocha-anyone/.
They often perch low in shady areas so unless they’re initially flying about, or you accidentally flush them, it may be difficult to locate one, even in their preferred habitat.
Mocha emeralds belong to a family of dragonflies known as Corduliidae. This family of odes is called emeralds because of their coloration. They’re usually brown or black with metallic green on parts of their bodies and have green eyes as adults.