 Y. orbiculata was described from a single part and counterpart compression fossil found at the Middle Ypresian McAbee Fossil Beds, Kamloops Group, near Cache Creek, British Columbia. The type specimens numbered UCCIPR L-18 F-749 and UCCIPR L-18 F-750 for the part and counterpart is currently preserved in the palaeoentomology collections housed at Thompson Rivers University, in Kamloops, British Columbia. Archibald, Cover, and Moreau coined the specific epithet from the Latin "orbiculatus", meaning "rounded" or "circular", in reference to the shape of the head. The species is discernible from the other two species of Ypresiomyrma by its notably rounded head capsule, and by the shape of the petiole which has a smoothly sloping convex shape with a node in the center. The petiole is similar in appearance to Prionomyrmex janzeni, and the propodeum is round. The queen is estimated to have been approximately 25 millimetres (0.98 in). The compound eyes are large and oval shape, but the antennae cannot be described due to poor preservation. The mandibles are large, containing seven to eight teeth. A well-developed stinger is also present.
