TRICERATOPS SERRATUS. 123 



The nasal horn core is wanting in the present specimen, as it was not ossified with the nasals. It projected upward and 

 forward. The nasal hones extend outside the superior branch of the premaxillaries, the lateral suture uniting the two being 

 nearly vertical. 



The present specimen is from the Ceratops beds of Wyoming in essentially the same horizon of the Laramie as the skull 

 of Triceratops Jiabellatus, to which reference has been made. 



FURTHER DESCRIPTION. 



This splendid skull may be further described as follows, and in the beginning I may state 

 that the character which has suggested the specific name is probably possessed in common, to 

 a greater or lesser degree, by all the species of the genus, or even of the family, and can not 

 therefore be considered as in any way distinctive. 



Notwithstanding its size, the skull pertained to an individual not fully adult, as shown by 

 the cranial sutures, most of which are still open, thus making it possible to determine with 

 accuracy the form and position of the various elements of the skull. The skull is complete, 

 except the nasal horn, the extremity of the predentary, a portion of the rostral, and the sum- 

 mits of the supraorbital horn cores, which are wanting. 



The nasals are in contact medially throughout their entire length, save at the extreme ante- 

 rior end, where they each send downward a short process. These downward-projecting proc- 

 esses diverge and embrace the elevated anterior portions of the premaxillaries. Posteriorly 

 the nasals pass beneath the anterior borders of the frontals, prefrontals, and lachrymals, with 

 which elements they articulate by underlapping and overlapping sutures, the posterior border 

 of the nasals being overlapped by the anterior borders of the elements mentioned. Interiorly 

 and posteriorly the nasals each send downward and forward a rather strong process, which 

 articulates below with the superior border of the maxillary for a short distance posteriorly and 

 for a longer distance anteriorly with the posterior projection of the premaxillary. Anteriorly 

 this inferior process of the nasal forms the posterior, and for a short distance the inferior, border 

 of the nasal opening. Posteriorly it forms the external superior border of the lachrymal fora- 

 men. The nasal horn is wanting, and its characters are therefore not determinable. Only the 

 sutural surface on the nasals is preserved, and from this it would appear to have been consid- 

 erably compressed transversely, with the antero-posterior diameter exceeding the transverse, 

 conditions somewhat similar to those that obtain in the nasal horn of Monoclonius splienocerus 

 of Cope. 



The rostral is rather small, with a strong median keel posteriorly separating two rather deep 

 pockets located one on either side for the reception of corresponding processes from the premax- 

 illaries. The rostral is lighter and less rugose than is usual in other skulls, but this may be due 

 to the immature age of the individual. 



The premaxillaries anteriorly are suturally united with the rostral and with each other, 

 while above they are embraced by short descending processes of the nasals, with which they are 

 also united by suture. Immediately beneath the nasal horn they each send upward a very 

 strong buttress. These support the nasals from beneath and give to this region the rigidity 

 that is essential to insure the most effective use of the nasal horn as an offensive and defensive 

 weapon. As in other genera and species, the premaxillaries form but an imperfect median sep- 

 tum and the external nasal openings are confluent. There are the usual number of laminae 

 and foramina in this region,which seem, however, to be subject to considerable individual variation. 

 They are best understood by a reference to PI. XXVII, where a side view of the skull is shown. 

 Posteriorly the premaxillaries articulate with the maxillaries, and superiorly they send upward 

 and backward a long, slender process, which is wedged in between the maxillary and nasal, 

 extending almost or quite to the anterior border of the lachrymal foramen, which in the present 

 species is situated between the nasal and maxillary instead of entirely within the maxillary, 

 as in Sterrholophus jiabellatus. 



The maxillary has the usual form. Its articulation with the premaxillary has already been 

 described. Supero-posteriorly the maxillary articulates with the jugal and forms the inferior 

 border of the lachrymal foramen. Owing to the imperfectly prepared condition of the type 



