There are three caballine crania from the Irvingtonian (300 BP?) of Hay Springs, Nebraska.

E. niobrarensis, Hay 1913, type skull UNSM 4999
I have studied only a cast of the type; Azzaroli mentioned the original appeared to have been heavily reconstructed.

E. hatcheri, Hay 1915, type skull UNSM 7868
It has been reconstructed as well but seems very similar to E. niobrarensis. The upper cheek teeth, however, are larger, and the protocones are not grooved.

The third one is AMNH 2725 and was referred by Gidley 1901 to E. complicatus. According to Gidley’s and Azzaroli’s figures and data it differs from both the precedent by a short and broad muzzle and very long protocones.