TITANOTHE'RIUM, an extinct genus of mammals from the "bad lands" of White river of Dakota, probably of the miocene formation. They were discovered by Dr. H. A. Prout, and named by Dr. Leidy titanotheriuni They belong to the extinct family brontotheridte, which includes as many as four genera, titanotheriurn, rneyacerops (q.v.), brontotherium, and diconodon. The best known genus is brontotherium, having the following characteristics: skull long and depressed, resembling that of the eros; large horn cores in front of the orbits, on the maxillary bones, and having large air cavities, nasal bones large and firmly ossified together; occipital condyles large ., 2 and widely separated; dental formula; z ; c pm 4-4 m— 3-3 . Upper in 2-2 1-1 1-1 3-3' 3-3 cisors small; canines short and stout with no diastema between them and the molars. The upper molars are large grinding teeth, often measuring 5 in. in diameter; brain cavity small in proportion to the skull, the cerebral hemispheres not extending over the cerebellum, and only to a small extent over the olfactory lobes; hemispheres compara tively large and much convoluted; cerebellum small, indicating clumsiness in motion; atlas or first cervical vetebra large and having great transverse extent; axis large, with massive odoutoid process; lumbar vertebrae smaller than dorsal. There were four
sacral vertebrae, and the caudal bones indicate a long and slender tail; limbs intermedi ate between elephant and rhinoceros; carpal bones shorter than in rhinoceros, support ing four stout toes, radius and ulna, and also tibia and fibula, separate; os calcis king, astragalus short. The hind feet had three toes of nearly equal size. None of the bones of the skeleton were hollow; nose probably flexible and tapir like, and not a true probos cis. These animals nearly equaled the elephant in size. The fossils of brontothe ricks are all as far as known from miocene beds of Dakota, Nebraska, Wyoming, and Colorado. Prof. Marsh, who discovered these extinct forms in these regions, remarks that the name titanotherium must give way to the previously applied name menodus.