PETERSON: THE AMERICAN DICERATHERES. 431 



remains representing D. cooki of these latter quarries are quite as abundantly 

 mingled with the remains of D. niobrarense in Quarry A. The latter quarry is 

 only a very short distance (300 yards) to the north of the main quarries and may 

 possibly represent a somewhat earlier time; or, more probably, the sediments 

 accumulated at this spot represent a different stream, which had its origin in, and 

 flowed through a locality more favorable to this species. 



10. Diceratherium cooki Peterson.-^ (Plates LX, LXI, LXII, fig. 1, LXVI, 

 figs. 2, 4). 



Synonyms. — Diceratherium arrikarense Barbour; D. schiffi Loomis; Acera- 

 therium stigeri Loomis; Diceratherium aberrans Loomis; D. loomisi H. J. Cook.^^ 



Ti/pe.— Skull of old male. CM. No. 1572. 



Paratypes. — Eight skulls, a number of lower jaws, and other skeletal material 

 C. M. Nos. 1573, 1575, 1581, 1841, 1848, 1853, 1855, 1888, 2408, 2443, 2799. 



Specific Characters. — Skull, especially of males, short and broad in its proportions. 

 Median lower incisor small. Crowns of the upper cheek-teeth coynpUcated. Crochet 

 often uniting with ectoloph in much worn teeth. Muzzle short. Horn-cores of males 

 prominent, but nasals not broad across the horns, and ends of nasals abbreviated. 

 Females varying from those with no horns to those with incipient horns. Postorbital 

 ridges seldom entirely meeting to form a sharp sagittal crest. Brain-case large. Occi- 

 put quite broad, of moderate height, and not overhanging. Premaxillaries short. 

 Margin of anterior nares much excavated, extending well back of the horn-cores and the 

 infra-orbital foramen situated close to the border. Posterior point of zygomatic arch 

 greatly expanded laterally and covered with heavy rugosities in fully adult or old males. 

 Basicranium short. Post-glenoid and paroccipital processes united to enclose the 

 external auditory meatus. Animal considerably smaller than D. niobrarense. 



General Description. 



Skull. 



As stated in the original description, this species rests on a number of skulls, 



lower jaws, and other skeletal material from which a male skull No. 1572 was 



originally selected as the type. In the first description it was stated that "the 



occiput is rather low, . . . the temporal ridges quite prominent, not uniting 



-^ Science (N.S.), Vol. XXIV, Aug. 31, 1906, p. 282-283; Annals Car. Mus., Vol. IV, 1906, p. 47, 

 PI. XV, text-figs. 12-13; Vol. VII, 1910, p. 274-279, PI. LXV; Loomis, F. B., Araer. Jour. Science, Vol. 

 XXVI, July, 1908, p. 58. 



-'D. arrikarense Barbour, Science (N.S.), Vol. XXIV, Dec. 14, 1906, pp. 780-781, figs. 1, 2; Acera- 

 therium stigeri Loomis, Amer. Journal Sci., XXVI, July, 1908, p. 60; Dieeralherium schiffi Loomis, I.e., 

 p. 57; D. aberrans Loomis, I.e., p. 59; D. loomisi Cook, Harold J., Neb. Geol. Surv., VII, p. 48-32, figs. 2-3. 



