Perissus thibetanus Pic, 1918 holotype has hind femora much longer than pygidium apex, my species has not.
In the other hand, Chevrolat (1863) described Ischnodora genus with " first hind tarsa 2 times longer than following ". In Gressitt key (1970), Perissus have "first hind tarsa at least 2 times longer than 2 + 3"
Ischnodora species described by Holzschuh have elytra more parallele side than Perissus species, with apex larger.