The skull of the leptictid insectivore Ictops, from the White River Oligocene, is redescribed, and compared with Echinosorex and other primitive Erinaceidae. It is concluded that Ictops is much more primitive than any known erinaceid, and at the same time possesses characters which indicate that the Leptictidae and Erinaceidae have specialized in divergent directions. The characters which Ictops shares with the Erinaceidae are almost wholly primitive insectivore characters, not indicative of special relationship. The Leptictidae are therefore removed from the Erinaceoidea and placed in a separate superfamily, the Leptictoidea.
A new classification of the insectivores is proposed, based on characters of the skull. The Lipotyphla are regarded as an order, with two suborders: (1)Erinaceomorpha, a primitive group consisting of the Leptictoidea and Erinaceoidea; (2)Soricomorpha, a specialized group, probably derived from an erinaceomorph ancestry, and comprizing the Tenrecoidea, Soricoidea and Chrysochloroidea. The chrysoehlorids are regarded as highly specialized derivatives of a soricomorph stock. The Macroscelididae, Tupaiidae, Lemuroidea and Dermoptera are interpreted as forming a natural group (Archonta), with an ancestry near the Erinaceomorpha. The Macroscelididae are related to the Tupaiidae, and thus to the Primates; they are in some ways more primitive than the Tupaiidae, and have developed in a divergent direction, in some respects paralleling the Erinaceidae. They are not closely related to the Lipotyphia, and are placed in a new order, Macroscelidea. The superorder Archonta thus consists of three orders: (1)Macroscelidea, (2)Dermoptera (3)Primates (including Tupaiidae).