Unidentified Striped Emerald (Somatochlora sp)

MINNESOTA: Cook Co; Superior National Forest, jct FR 170 (The Grade) and FR 455 - male - 7 August 2010

This male Emerald hung up about 25 feet above me in an aspen.  When I tried to climb a nearby tree to get better photos, it flushed.  It appears to have no or very reduced thoracic spots.  At first I thought it likely that it was a Williamson's Emerald (Somatochlora williamsoni), but the appendages seem wrong for that species.  I realize that there may not be enough details in these photos to make an ID, but others with more experience may be able to provide more insight.