ARSINOITHERIUM (from the Egyptian queen Arsinoe), a gigantic horned mammal from the Middle Eocene beds of the Fayum, Egypt, representing a sub-order of Perissodactyla called Barypoda. The skull carries a huge pair of horn-cores above the muzzle, which seem to be the enlarged nasal bones, and a rudi mentary pair farther back; the front horn-cores, like the rest of the skull, consist of a mere shell of bone, and were probably clothed in life with horny sheaths. The teeth form a continuous even series, the small canines being crowded between the incisors and premolars; the crowns of the cheek-series are tall (hypso dont), with a distinctive pattern. Although the brain is relatively larger, the bones of the limbs, especially the short, five-toed feet, approximate to those of the Amblypoda and Proboscidea (qq.v.); but in the articulation of the astragalus with both the navicular and cuboid Arsinoitherium is nearer the former than the latter. It is probable, however, that these resemblances are mainly due to parallelism in development, and are in all three cases adaptations necessary to support the enormous weight of the body. On the other hand, the marked resemblance of the struc ture of the tarsus is probably indicative of descent from nearly allied condylarthrous ancestors (see PHENACODUS).
See C. W. Andrews, Descriptive Catalogue of the Tertiary Verte brate of the Fayum, British Museum (1906).