SYNOPSIS. 215 



Marsh, Fifth Amiiial Report of the U. S. Geolooical Survej', (figures from the present 

 volume, viz:) tig. 75, p. 275; 85, p. 279, 1884. 



The skull in this species presents some striking- peculiarities. The 

 maxillary protul)erances are placed well back, and are much above the 

 socket for the weiik and slender canine tooth (figure 48, page 43). They 

 are directed upward and outward, and are greatly excavated within, and 

 below, as shown in figure 191. The parietal protuberances are well 

 developed, and are also excavated near the base. The anterior face, as far 

 as preserved, shows no distinct indication of a sharp ridge rising- on the 

 frontal bone in front of the protuberance, as in Dinoceras laticeps (number 

 1202), but the parietal protuliernnces seem to have risen abruptly, as in 

 Thioceras infjens. They are fiattened behind, but are scarcely expanded 

 transversely, as in the males of this t3'pe. The zygomatic process of the 

 s(iuaniosal is slender, and presents a decided pit for the posterior end of 

 the malar, just in front of the glenoid cavity. 



The lower jaw (figure 38, page 37) is elongated, and presents a small 

 and weak pendent process, for the protection of the small and slender 

 canine tusk (figure 48, page 43). This tusk has a nearly straight root, 

 which suddenly contracts at the apex into a small orifice. The position 

 of its socket is well in front of, and below, the maxillai-}' horn-core, and 

 unlike that of any other specimen in the Museum. 



This species is based upon a specimen (number 1256, female) obtained 

 by Mr. J. Heisey, at Red Dog Jiuttes, Wyoming, in June, 1876. 



The remains of the type of this species consist of portions of the 

 skull, lower jaws, etc. 



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



The known remains of this species are in Yale College Museum. 



Tiiioceras puftiiax, Marsh. 



(Plate XIX.) 



Woodcuts: 5, p. 13; 18, p. 19; 19, p. 21; 24, p. 25; 29, p. 27 ; 52, p. 45; 67, p. 6.3. 



Marsh, Fifth Annual Re])ort of the \J. S. Geological Survey, (figures from the present 

 volume, viz:) fig. 42, p. 258; 5::), p. 26.3; 54, p. 264; 59, p. 267; 64, p. 269; 89, 

 p. 282; 104, p. 290, 1884. 



The type specimen of this species (numl)er 1044) was an individual 

 of moderate size, and a male. The skidl is short, and, seen from above 

 strongly Avedge-shaped. The nasal protuberances are small, high, and 

 widely separated. The maxillary elevations are somewhat in front of the 

 diastema. They are robust and reciu-ved. The parietal jjrotuberances are 

 of moderate height, and transversely compressed at their summits. The 

 premaxillaries are widely separated in front. The palato-maxillary 

 foramen is opposite the second premolar. The posterior nares open 

 iipAvard through oval apertures, but little behind the bony palate. The 



