102 



THE CERATOPSIA. 



I can add nothing of importance to Professor Marsh's original description of the type, 

 except to give the more important measurements. These are as follows: 



Measurements ofCeratops montanus. M 



Height of frontal horn core _ 220 



Antero-posterior diameter of same at base 93 



Transverse diameter of same at base .'. _ 88 



Transverse diameter of occipital condyle . 71 



The principal characters of the type material are well shown in figs. 103 a and 104, a and 

 from these and the above description it is clear that the genus Ceratops must rest on the char- 

 acters displayed by the occipital condyle and the frontal horn cores, neither of which elements 

 are represented in the actual type of the genus Monoclonius of Cope. If the frontal shown in 

 fig. 75, bearing the diminutive horn core which was subsequently associated by Cope with the 

 type, though evidently pertaining to a much smaller individual, be admitted as a cotype, and 

 therefore to some extent, at least, diagnostic of the genus Monoclonius, there would still be 

 good reasons for considering Ceratops montanus as both generically and specifically distinct 



B 



Fig. 103.— Supraorbital horn cores of the type of Ceratops montanus Marsh (No. 2411, U. S. National Museum) in their proper position. 



A, O blique back view; B, anterior view. One-fourth natural size. 



from Monoclonius crassus, for such striking differences as are shown in these two types of frontal 

 horn cores are certainly suggestive of other and even more important structural differences 

 in the skull and other portions of the skeleton. However, the full discussion of such questions 

 must be left for that portion of this volume devoted to a revision of the genera and species. 

 The squamosal figured by Marsh 6 as pertaining to Ceratops montanus, but originally 

 described in the above quotation as a dermal plate, was found by the present writer many 

 miles from the locality which furnished the type. It may or may not pertain to that genus 

 and species. Judging, however, from the character of the squamosal in Ceratops {Monoclo- 

 nius) canadensis Lambe, where the supraorbital horn cores are strikingly similar to those of 

 the present species, it seems probable that Marsh was in error in referring this squamosal to 

 C. montanus. 



a In figuring the type of Ceratops montanus, Marsh mistook the external lateral view of the supraorbital horn core for the posterior. For- 

 tunately a portion of the orbit is present, making it possible to determine the position of the horn cores with certainty. In fig. 103 these horn 

 cores are shown in their proper positions, which is somewhat different from that assigned them by Professor Marsh. 



b Am. Jour. Sci., vol. 43, 1892, pi. iii, fig. 3. This monograph, PI. I, fig. 1. 



