426 0. G. Marsh — Characters of the genus Coryphodon. 



which may be called Coryphodon hamatus. It indicates an ani- 

 mal somewhat larger than a tapir. The more important char- 

 acters derived from an examination of this cranium, and some 

 other remains of the same genus, are as follows : 



The skull is elongated, the facial portion being most pro- 

 duced. A basal line extending from the lower margin of the 

 foramen magnum along the palate to the end of the premax- 

 illaries is nearly straight. The zygomatic arches are much ex- 

 panded, but the malar is comparatively slender, and joins the 

 maxillary in front of the orbit. The latter is of moderate size, 

 and confluent with the large temporal fossa. The general form 

 of the skull is indicated in the cut given below, figure 2. The 

 maxillaries are massive, and on the sides behind the canines 

 are deeply indented, giving a marked constriction to this part 

 of the skull. The lachrymal forms the anterior border of the 

 orbit, and its foramen is inside the orbital margin. The nasals 

 are quite slender in front, and broad posteriorly. The pre- 

 maxillaries are expanded transversely, giving a wide anterior 

 narial aperture. The anterior palatine foramina are small, (fig- 

 ure 2.) The posterior nares extend forward between the last 

 upper molars. The dental formula is as follows : 



Incisors—; canines—; premolars—; molars--; X2=44. 



The teeth agree in all generic characters with those figured as 

 Coryphodon by Owen and Hubert. The occipital condyles are 

 well separated, and there is a condylar foramen. Between the 

 basisphenoid and the periotic, there is a large opening, partially 

 due to the divergence downward of the inner faces of the lat- 

 ter bones. There is a strong paroccipital process, and a post- 

 glenoid process, which varies in size in different species. In 

 Coryphodon hamatus, it is long, and curved forward, and to this 

 the specific name refers. The skull as a whole presents strong 

 Perissodactyle characters. 



The brain cavity in Coryphodon is perhaps the most remark- 

 able feature in the genus, and indicates that the brain itself 

 was of a very inferior type. It was quite small, as in all 

 Eocene mammals, but its most striking features were the small 

 size of the hemispheres, and the large expanded cerebellum. 

 The form and relative size of these are shown in the accom- 

 panying cuts, figures 1 and 2. 



The olfactory lobes were large, and entirely in advance of the 

 hemispheres. They were bounded in front by a well ossified 

 cribriform plate, and partially separated by a vertical bony sep- 

 tum. The cerebral lobes were ovate in form, and very small, a 

 transverse section exceeding but little that of the medullar 

 opening. In shape and relative size, the hemispheres and ollac- 



