176 Marsh — Principal Characters of the Protoceratidce. 



interval between the canine and second premolar, as shown in 

 the figure cited. The remaining upper premolars correspond 

 closely with those of Protoceras in form, and this is true, also, 

 of the molars. The lower incisors of Galops are small and pro- 

 cumbent. The canine also was small, and probably similar in 

 form to the incisors. The first lower premolar is caniniform 

 in shape, with a single root, and a sharp compressed crown, 

 which came nearly in apposition to the superior canine. The 

 remaining lower premolars and molars agree closely except in 

 size with those of Protoceras. 



The remains of Galops now known all appear to have per- 

 tained to females, and this naturally suggests the question — what 

 the male skull was like, and especially whether it was provided 

 with horns. The probabilities at present are in favor of the 

 latter view, but it must be left to future discoveries to settle 

 that point. 



All the known remains of Protoceras and Galops are from 

 the upper Miocene of South Dakota. The horizon, which is a 

 definite one, has been appropriately called by Dr. Wortman the 

 Protoceras beds. They appear to be identical with the series 

 in Oregon which the writer had previously named the Miohippus 

 beds, as that genus and several others are common to both 

 regions. 



Yale University, New Haven, Conn., July 24, 1897. 



EXPLANATION OF PLATES. 



Plate II. 

 Male skull, with lower jaw, of Protoceras celer. Marsh; oblique side view. 

 Three-fourths natural size. 



Plate III. 

 The same skull ; seen from the left side. Three-fourths natural size. 



Plate IV. 

 The same skull ; seen from above. Three-fourths natural size. 



Plate V. 

 The same skull ; seen from below. Three-fourths natural size. 



Plate YI. 

 Figure 1. — The same skull; seen from in front. 



Figure 2. — Front of skull of Protoceras comptus, Marsh ; seen from below 

 young female, showing deciduous dentition. 



Both figures are three-fourths natural size. 



Plate YII. 

 Figure 1. — Skull, with lower jaw, of Calops consors, Marsh; seen from the left. 

 Figure 2. — The same skull ; seen from above. 



Figure 3. — Natural brain cast of Protoceras celer ; female ; side view. 

 Figure 4. — The same ; seen from above. 



The figures are all one-half natural size. 



[To be continued.] 



