SYNOPSIS. 205 



The face on the zygomatic pi'ocess of the squamosal for the malar is 

 broad and flat, and does not end in a pit, for the posterior end of the 

 malar bone. 



In this species, the brain occupies a very oblique position in the skull, 

 as shown in the accompanying woodcut, figure 178. In the section of the 

 cranium, the sutures defining the anterior and posterior limits of the 

 parietal bones along the median plane of the skull are clearly shown. 

 The fronto-parietal suture also (figure 178) is apparent on the superior 

 surface of the skull, above the anterior part of the cavity for the cerebral 

 hemispheres, as in Dinoceras distans (number 1601). The suture limiting 

 the parietal posteriorly is evident in the same section. It is behind the 

 cerebral cavity, but cannot be traced with certaintv on the upper surface 

 of the skull. 



The type specimen (number 1574) of this species was obtained by 

 Mr. J. Heisey, eight miles south of Dug Springs, Wyoming, in 1876. 



This specimen consists of a skull, etc. 



The geological horizon is in the Dinoceras beds of the Middle Eocene. 



The only known remains of this sjjecimen are in Yale College Museum. 



Tiiioceras aimecteiis, Marsh. 



Woodcuts: G, J). 13; 21, p. 21; 36, 37, ]'. 36. 



Marsh, Fifth Annual Report JJ. S. Geological Survey, (fitjures fnnn the present Tohime, 

 viz:) fig. 43, p. 258; fig. 56, j). 264; tig. 73, 74, p. 274, 1884. 



The skull in the type of this species (number 1043) agrees generally 

 in size and form, as far as preserved, with that of Thioccras btgens, (number 

 1041). The canine tusk runs somewhat forward in number 1043, and the 

 premaxillaries appear less robust. The palato-maxillary foramen is near 

 the front premolar, not well in front of it, as in Tinoceyus hifjens. The 

 upper canine (page 21, figure 21) has, on its outer side, a large, somewhat 

 heart-shaped, Avorn surface. 



The lower jaw in tins species is slender, and bears a well developed 

 process running downwai'd and forward, and terminating in an oblique, 

 nearly straight margin. Tlie coronoid process is pointed. 



The first dorsal in this sjiecimen is proportionally shorter than in 

 Tinoceras anceps, with the lateral faces for its ribs more a})])roximate. The 

 length of the flooi" of the neural canal is to the length of the under surface 

 of the centrum as 3 to 4, and a similar proportion in the adjoining 

 vertebra indicates an upward^ciirvature in the neck at this point. 



