This one was surprisingly straightforward to identify. The lack of a sclerite at the base of the lateral hump narrows the field quite a bit, and the other options followed fairly obvious characteristics to Clostoeca, which only has one species, Clostoeca disjuncta.
Beardius on Aug 1, 2008August 1st, 2008, 6:45 am EDT
This looks to be either Hexagenia or Litobrancha based upon the frontal process being rounded and not forked. Probably is Hexagenia based upon where it was collected and Hexagenia being so widespread and common, but I cannot tell from the photo if the gill on the first abdominal segment is forked or single from these photos.