Post update: What is it — emerald or skimmer?

An exuvia from a Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

The presence of a ventromedial groove in the prementum suggests this specimen is a member of Family Corduliidae (Emeralds) and in fact it is.

Congratulations to Douglas Mills, who correctly identified the family of this specimen.

Going with corduliidae for the groove. It’s got impressive crenulations — I had to double check they weren’t jagged and this was a trick question 🙂 Source Credit: Douglas Mills.

Douglas successfully avoided the trap that was set when I chose to use a specimen that features deeply-scalloped crenulations along the margins of the palpal lobes. According to Kevin Hemeon, member of the “Odonate Larvae and Exuviae” Facebook group, crenulations like these are a characteristic field mark for Genus Neurocordulia (Shadowdragons) in the Family Corduliidae (Emeralds).

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Copyright © 2021 Walter Sanford. All rights reserved.

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