Page:Parasaurolophus walkeri, a new genus and species of trachodont dinosaur.pdf/12

8 It will be seen from these measurements that the head, exclusive of the remarkable crest, is very much smaller than in Saurolophus; in fact, the proportions are more like those of Corythosaurus, in which the quadrate is of the same length (280 mm.) and the mandible nearly the same (669 mm.). In Stephanosaurus, likewise, the measurements of the critical elements of the head are very similar–275 mm. for the quadrate, and 645 mm. for the mandible.

Premaxillary—The premaxillaries form the characteristic duck-bill as in other genera of trachodonts: they are excavated in wide narial depressions anterior to the nares proper. This depression is ﬂoored throughout as in Corythosaurus, and there is a complete internarial septum. Whether this septum is formed by ascending processes from the premaxillaries or whether it is part of the nasal, it is impossible to say on account of the state of preservation of the parts. The only suture visible is a median one in the internarial bar. This can be traced forward a little in advance of the transverse line joining the anterior margins of the two narial depressions. Here it forks, turns outwards, and is lost. There is indistinct evidence that it turns back again and cuts the anterior margin of the narial depression about one-third of the distance across that opening. This arrangement is distinctly different from that in Saurolophus, where ascending processes from the premaxillaries separate the nasals along the mid-line of the internarial bar.

Posteriorly also a distinct suture between premaxillary and nasal cannot be deciphered with certainty; it is possible, however, that a suture runs backward from the posterior point of the narial opening, turns outwards and then forward. and terminates at the deep suture above the maxillary. If this line is really the premaxillary-nasal suture, it indicates a condition somewhat like that of Parasaurolophus The most posterior point of this supposed suture is 460 mm. from the middle point of the beak and the termination on the premaxillary-maxillary suture 360 mm. from the same point.