174 Marsh — Principal Characters of the Protoceratidce. 



" The dentition preserved is selenodont andbrachyodont, with 

 only three premolars and three molars.* The first premolar is 

 mnch compressed transversely, and has but a slight inner lobe. 

 The second premolar is triangular in outline, the inner lobe 

 being much more developed. The last premolar has this lobe 

 expanded into a strong cusp, and the crown thus becomes^broader 

 than long. The true molars have two inner cusps, each with a 

 basal ridge. The outer crescents have a median vertical ridge. 

 The enamel of the molar series is more or less rugose. There 

 was a wide diastema in front of the premolars. 



" The posterior nares are situated far forward, the anterior 

 border being opposite to the posterior cusp of the second true 

 molar. The glenoid facet is large and convex, but the post- 

 glenoid process is quite small. The paroccipital processes were 

 well developed, but there were apparently no auditory bullae." 



A number of other female skulls, some of them in excellent 

 preservation, have since been obtained from the same region in 

 which the type was found, and a study of these makes clear the 

 main points of their structure. It is not quite certain to which 

 of the three species of Protoceras now known some of these 

 skulls should be referred, but further investigation will doubt- 

 less determine this point, as the present material in the Yale 

 Museum is apparently sufficient for this purpose. 



The Skull of Calops. 



The small artiodactyle described by the writer in 1894, under 

 the name Galops cristatus, is from essentially the same geologi- 

 cal horizon in South Dakota in which Protoceras was found. 

 As stated in the first description, Calops possesses characters 

 indicating a near ally of Protoceras, and as the resemblance has 

 proved even closer in more perfect specimens since discovered, 

 denoting that the two genera belong to the same family, it 

 may be well to quote here the main points of the original 

 description, f 



"The type specimen is a skull in fair preservation, indicating 

 a fully adult animal, which when alive was about half as large 

 as a goat. In its general form and in most of its characters, 

 this skull agrees so closely with the type of Protoceras as to 

 suggest at once some affinity between the two. The dentition 

 preserved in the premolar and molar series is essentially the 

 same. The high maxillary plates joining the short, pointed 

 nasals ; the deep lachrymal fossa ; and the posterior orbit 



*More perfect specimens since discovered prove that there were four premolars, 

 the first being absent in the type. 



fThis Journal, vol. xlviii, p. 94, July, 1894. 



