218 Reviews — Prof. 0. C. Marsh's Dinocerata. 



elevated and sub-quadrate in outline. It varies much in shape and 

 size in the different genera and species, and two of the principal 

 forms are represented (see Figs. 2 and 3). 



" The malar bone completes the anterior portion of the zygomatic 

 arch, extending to the front of the orbit. I'he suture uniting the 

 malar with the maxillary remains distinct till adult life, and may 

 usually be traced, even in old animals. This forward extension of 

 the malar bone is a general ungulate character, and quite different 

 from what is seen in the Proboscidians, where the malar forms the 

 middle portion only of the zygomatic arch. 



" The lachrymal is large, and forms the anterior border of the 

 orbit (see Fig. 1). It is perforated by a large foramen. In Dino- 

 ceras mirabile, this is oval in outline, with the apex above. The 

 base of the lachrymal is excavated for the posterior opening of the 

 large antorbital foramen. 



" The large canine tusk is entirely inclosed in the maxillary bone, 

 and in the genus Dinoceras, its root extends upward into the base 

 of the maxillary horn-core. In all known Dinocerata, there is a 

 diastema between the upper canine and the premolars. 



" The premaxillary bones are edentulous, and, even in young 

 specimens, contain no teeth. The premaxillaries vary much in form 

 in the different genera and species. 



" Two of the principal forms are shown in Figs. 6 and 7. 



"The palate is very narrow and much excavated, especially in front. 

 The bony palate extends back as far as the last upper molar, and in 

 some specimens beyond. It is deeply excavated on each side in 

 the region of the diastema, and near the posterior part of each ex- 

 cavation on either side is situated a large foramen, which may be 

 called the palato-maxillary foramen (Figs. G and 7, b). 



" In the type of Dinoceras, the palatine fossa of the posterior nares 

 is roofed over, so that the passage from the palate into the lai-ge 

 nasal cavities above leads forward and upward, as shown indistinctly 

 in Figure 7. In Tinoceras ingens and Tinoceras pugnax, the roof of 

 this fossa is excavated in front by a pair of oval apertures, and, 

 through these, the posterior nares open directly upward, as repre- 

 sented in Figure 6, e. 



" The Loioer Jaw. — The lower jaw in Dinoceras is as remarkable 

 as the skull (see Figs. 8 and 9). Its most peculiar feature in the 

 male is a massive decurved process on each ramus, extending down- 

 ward and outward. These long, pendent processes were apparently 

 to protect the upper canine tusks, which would otherwise be very 



liable to be broken In the female, this process is much 



reduced in size, but is quite sufficient to protect the diminutive tusk 

 which overlaps it. 



" Another remarkable feature in the lower jaw of the Dinocerata 

 is the posterior direction of the condyles, hitherto unknown in 

 Ungulates. 



" In the genus Dinoceras, there are three incisor teeth, and a small 

 incisiform canine on each side, forming a continuous series at the 

 front extremity of the lower jaw. These are all of moderate size, 



