Measurements of the Type Skull of Diceratosaurus lævis Moodie. mm. Length of skull along median suture 37 Length from muzzle to tip of horn 50 Width between tips of horns, estimated 40 Width of orbit 7 Length of orbit 10 Width of skull across the orbits 30 Interorbital width 6 Length of nostril opening 2 Width of nostril 1 Diameter of the pineal foramen - 1 =Diceratosaurus robustus Moodie.= Moodie, Jour. Geol., XVII, No. 1, p. 67, fig. 15, 1909. Moodie, Bull. Am. Mus. Nat. Hist., XXVI, art. XXV, p. 355, pl. lxiii, fig. 2, 1909. Type: Specimen No. 8611 G, American Museum of Natural History. Horizon and locality: Linton, Ohio, Coal Measures. The present species is indicated by the left portion of a cranium representing a large individual. The characters of the skull are so clearly marked that it seems worthy of description. The presence of horns as given in the restoration of the skull (fig. 24, B) is based on the analogy with the other two species of this genus, in both of which horns are present. The generic determination of the species is based on the large size of the postorbital, which is essentially characteristic of the other species of _Diceratosaurus_. The characters which distinguish the species from others of the genus are the large postorbitals and the small parietals, which are excluded from union with the postfrontals on account of the large size of the frontal. In the other two known species the frontal is small and the parietal comes forward to join the postfrontal. The present species exhibits a skull which is nearly twice as large as that of _D. lævis_ and nearly three times the size of the skull of _D. punctolineatus_.