282 



SCIENCE. 



[N. S. Vol. XXIV. No. 609. 



MEASUREMENTS. 



Greatest length of skull, approximately 450 



Length of skull from occipital condyle to and 



including P- 370 



Length of skull from occipital condyle to M^ . 190 



Greatest transverse diameter of skull 235 



Greatest transverse diameter of brain case . . 130 



Greatest transverse diameter of f rontals .... 150 

 Greatest transverse diameter of occipital 



condyles 103 



Greatest transverse diameter of palate 68 



Vertical diameter of the orbit 60 



Length of 2d, 3d and 4th premolars and the 



molar series 185 



Antero-posterior diameter of P' 26 



Transverse diameter of P- 29 



Antero-posterior diameter of P* 32 



Transverse diameter of P* 36 



Antero-posterior diameter of M^ 39 



Transverse diameter of M^ 37 



Antero-posterior diameter of M^ 35 



Transverse diameter of M^ 39 



Diceratherium CooTcif 



This species is very abundantly represented 

 in the Agate Spring quarry, and there are at 

 present some forty or fifty skulls, jaws, and 

 other portions of the skeleton representing it 

 in the Carnegie Museum. Only a small por- 

 tion of this material has been freed from 

 the matrix. Preliminary observations have 

 been made upon eight skulls, to one of which 

 the lower jaws are attached. Of this series 

 a specimen designated as No. 1,572 (Carnegie 

 Museum CatalogTie of Vertebrate Fossils) is 

 selected as the type. The skull represents 

 an animal much smaller than D. niohrarensis. 

 The top of the skull is perfect, but the an- 

 terior part of the maxillaries is wanting. 

 The premaxillaries are lost, and the base of 

 the skull has received considerable injury. 

 Only the first and second molars are present 

 on the right side, while the dentition of the 

 left side, except P\ is present. 



The principal characters of the tyi)e are as 

 follows : Skull mesaticephalic. 



10 4 3 



-'2' ^0' -^3' -^S" 



Brain case relatively as large as, or even 



larger than in Diceratherium niohrarensis. 



' In recognition of the kindness of Mr. James 

 H. Cook to the field parties sent out by the Car- 

 negie Museum. 



The occiput is rather low. The inion is broad, 

 with a wide posterior emargination. The 

 temporal ridges are quite prominent, not uni- 

 ting to form a sagittal crest, but continuing 

 separate as far as the inion, where they join 

 the lambdoidal crest. The frontals are broad, 

 especially over the orbits, and are slightly 

 convex from side to side. The nasals are 

 each provided with a heavy, ovate, rugose horn- 

 core near their free extremities. The nasals 

 are very abruptly pointed in front of the horn- 

 cores, and are at this point directed down- 

 ward and slightly forward The dorsal sur- 

 face of the skull as a whole is saddle-shaped, 

 as in Diceratherium niohrarensis, but the 

 frontals in the present species are relatively 

 considerably broader. The zygomatic arch is 

 quite heavy, with a rugose enlargement at the 

 posterior angle. The narial openings are 

 large, the posterior orifice extending forward 

 to a point opposite the line between M^ and 

 M^. The foramen magnum is rather large 

 in size. The orbit is relatively smaller than 

 in Diceratherium niohrarensis. The infra- 

 orbital foramen is placed above P^ 



The base of the skull presents some inter- 

 esting features showing a wide difference from 

 the first species which is described in this 

 paper. Of these the most important is the 

 complete enclosure of the ear by the post- 

 glenoid process and the mastoid, which touch 

 each other in a manner somewhat similar to 

 that described in Ceratorhinus according to 

 Cope.^ Purthermore, the dentition in the 

 present species is distinctly more specialized 

 than in Diceratherium niohrarensis, so that 

 together with the small size of the skull it 

 shows a degree of resemblance to European 

 forms as Diceratherium minutum Cuvier. 

 The first premolar in the present species is 

 reduced in about the same proportion as that 

 in the species previously described. The 

 crotchet of M^ has nearly closed the interspace 

 between the cross-crests, and in very old indi- 

 viduals it is in fact an enclosed cavity of the 

 tooth. 



Characters worthy of being noted are de- 

 rived from a number of lower jaws belonging 



^American Naturalist, Vol. XIII., p. 771, 1879. 



