Two Eocene age species found in Western North America were placed into the genus, H. dillhoffi and H.

[2] The specific epithet dillhoffi is a patronym honoring Richard Dillhoff, who found and donated a number of fossils for research, including the type specimen, and for his support of paleoentomology.

The family received a full technical description 19 years later by the German entomologist Rainer Willmann and the circumscription was emended by Archibald in 2010 to reflect the second species.

Fortiholcorpa has medial wing veins notably different than those of Holcorpa and an 8th abdominal segment only slightly longer than the 7th.

Conversely, Miriholcorpa was not placed due to the hind wings not having discernible forking of the median vein into 5 branches.

The elongated abdomen of Holcorpa is not seen in the family Eorpidae, and by the much more curved nature of "Radial1" vein is not seen in Dinopanorpidae.

The 6th abdominal segment seems to be missing spurs, possibly lost during preparation, but the angle formed by them is wider than those of H.