172 Marsh — Principal Characters of the Protoceratidce. 



The teeth of the lower jaw of Protoceras are indicated in 

 Plate II, and the full series is shown. The three incisors are 

 directed well forward, and diminish in size from the first to the 

 third. The still smaller canine is situated close to the last 

 incisor, and is similar in form. A long diastema follows, and 

 gives the upper canine freedom of motion. The first premolar 

 is somewhat similar to the corresponding one above, hut is 

 larger and directed more forward. A still longer interval 

 separates the first and second lower premolars, the latter begin- 

 ning the continuous molar series. The second premolar has 

 the crown much compressed, while the third and fourth are 

 triangular in form. The three true molars have the usual cres- 

 cents corresponding to those above, but no inner cingulum. 



The upper molar teeth of the female skull are shown in 

 figure 7, below, which represents the type of the genus. On 

 Plate VI, figure 2, the upper dentition of Protoceras comptus 

 is represented, the type specimen figured being the skull of a 

 female not yet adult.* The last three deciduous teeth are here 

 still in use, the first and second true molars are in position, 

 while the last had not yet come into place. 



The Brain. 



The brain in Protoceras was of good size, not diminutive as 

 in the early ungulates. It was, moreover, well convoluted for 

 a Miocene mammal, and forms an interesting addition to our 

 knowledge of the brain development in Tertiary Mammalia. 



The natural brain cast figured in Plate VII, figures 3 and 4, 

 is from an adult female skull, and represents accurately the 

 brain cavity of this individual, except the small space occupied 

 by the olfactory lobes. The latter were well developed. 



The Female Skull. 



The type species of the genus Protoceras, as already stated, 

 was the skull of a female, and it may be well to repeat here its 

 essential features as given in the original description already 

 cited. In figures 6 and 7 below, most of the main characters of 

 this type specimen are represented. 



"In general form and proportions, this skull is of the rumi- 

 nant type. Its most striking feature is a pair of small horn- 

 cores, situated, not on the frontals, but on the parietals, immedi- 

 ately behind the frontal suture. These prominences were thus 

 placed directly over the cerebral hemispheres of the brain. 



* This Journal, vol. xlviii. p. 93, July, 1894. 



