I think not. Compare genus key on family info page - Heb*rus should have the 4th segment constricted, making antennae to appear 5-segmented, while Merra*gata should have distinctly shorter antennae . . .

You are correct. In a frenzy of putting together a Heteroptera workshop for the Maine Entomological Society and coincidentally correcting the Veliids, I got these two genera mixed up.

Although I hate using keys outside of my own state or area, I decided to try and find a general Hebridae key, and found one at ftp://ftp.dep.state.fl.us/pub/labs/biology/biokeys/heteroptera.pdf. It's a key of the aquatic "hemiptera" of Florida, and had all three genera of Hebrida, so I though I'd take a look. It seems since it has 4 antennal segments, and the 4th segement is about the same width (not obviously wider) than the others, it sends directly to Lipogomphus, the only species in this genus is L. brevis. I hope that this can place it, but any help would be appreciated.

Lipogomphus is a Southern group... not South Dakotan... this can only be Hebrus

to hebridae for now; maybe an expert can confirm your species ID.

are you sure on only 4 antennomeres? looks like 5 in this photo.

The 4th antennal segment has an indent in the middle, but is not entirely separated...I belive I saw it in the key somewhere...