108 



THE CERATOPSIA 



The epijugals are quite conspicuous, almost horn-like processes, very suggestive of those of 

 Pentaceratops. The crests in the two genera are also somewhat alike, with elongate fenestrae. The 

 nasal horns, however, are very dissimilar. That of Anchiceratofs, on the other hand, resembles the 

 nasal of Arrhinoceratops much more closely, even to the sharp upper edge. The crests in these two 

 genera are also somewhat similar except at the rear, for that of Arrhinoceratops ^ lacks the epoccipitals 

 and the two knob-like prominences on the rear of the parietals. In proportions, Arrhinoceratofs 

 has a relatively short, deep muzzle while that of Anchiceratofs longirostris is elongate, as the name 

 implies. 



Measurements of Skull of Arrhinoceratops 

 (After Parks) 



Length, from tip of rostral to extremity of crest 1520 mm. 



Width, across tips of epijugals 700 



Width, across posterior margin of crest 830 



Width, across anterior end of crest 834 



Maximum width of crest 1080 



Tip of rostral to occipital condyle 718 



Occipital condyle to rear of crest 810 



There is but one species, as but two specimens only are as yet referable to this genus, one of 

 which is unprepared, hence specific characters as distinguished from those of the genus cannot be 

 determined. The relationship of Arrhinoceratofs to other genera is not evident. It belongs to the 

 group characterized by long squamosals, and on this basis alone would lie nearer the Chasmosaurus- 

 Torosaurus phylum than the Monoclonius-Triceratofs line in which the squamosal is either short or 

 of medium length (see p. 27 and Fig. 3). This is in accordance with Doctor Parks' opinion. 



Genus PENTACERATOPS Osborn 

 Pentaceratops sternbergii Osborn 55 



PL V, B; Text Fig. 39 



Holotype: No. 6325 A.M.N.H.; skull without lower jaw (skeleton discarded). 



Horizon: Fruitland formation. 



Locality: Nine miles northeast of Tsaya, New Mexico. 



Collector: C. H. Sternberg, 1922. 



Generic characters are stated to be : "One nasal horn, two prominent anteroverted postorbital 

 horns, two lateral jugal osseous horns; with elongate narrow fontanelle in the dermosupraoccipital 

 crest. Borders of the crest moderately sculptured. Generally intermediate in character between the 

 Eoceratops and Anchiceratofs types of skull, in size and proportion approaching the Triceratofs type, 

 in the large fontanelle resembling TorosaurusP 



Osborn says further: "Comparing this skull with other specimens of ceratopsians, we observe 

 the following resemblances and differences. 



"(1) The fontanelles are elongate, instead of circular as in Monoclonius and Torosaurus 

 (Hatcher-Lull Monograph, 1907, PL II). 



"(2) The postorbital horns rise directly above the center of the orbit and curve gently forward, 

 a different position and inclination from that observed in the types described by Hatcher and Lull 



{of. cit., PL V). . 



"(3) The skull of Pentaceratofs, when compared in profile with that of Diceratops and Iri- 

 ceratofs {of. cit., PL XLIV), shows that the lateral horns are borne upon the jugals. They project 

 much more widely than the prominences on the jugals of Triceratofs brevicornus [op. cit., PL 

 XLII]. The skull of Pentaceratops sternbergii ... is relatively more elongate than that of Tricera- 



55 Osborn, H. F., 1923. 



