Examination of the tibia may be necessary to confirm identifications.
The bottom image of Catocala piatrix shows a brown head and thorax rather than the grey prevalent in the other two species. The subreniform spot is usually large and open as opposed to that shown in the bottom image where it is relatively small and closed.
C. piatrix is characterized by the pale area located anterior to the subreniform spot and extending to the costa. Overall ground colour of the forewing is more of a uniform grey-brown.

Catocala subnata female, courtesy of Pierre Legault.

Catocala neogama August 9, 2004, St-Anne de Bellevue,
Montreal, Quebec,
females, attracted to bait, courtesy of
Pierrre Legault.

Catocala neogama August 9, 2004, St-Anne de Bellevue,
Montreal, Quebec,
females, attracted to bait, courtesy of
Pierrre Legault.

Catocala piatrix Klingerstown, Pensylvania, 10-08-1992,
male, courtesy of Pierrre Legault.
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