478 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



The skull of the Texas specimen is moderately elongated, not 

 nearly so much so as that of Trinacromerum or Polycotylus, but 

 more so than is the skull of the known species of Elasmosaurus. The 

 temporal fossae are unusually large, the zygomatic bars remarkably 

 slender posteriorly, and the parietal bone is not elevated into a thin, 

 high crest as is the case with the skulls of the genera mentioned, 

 but is low, straight, and obtusely rounded on its upper surface. 

 The teeth are fewer, less elongated than in those genera; they are 

 coarsely striate. All parts of the skull are present, save the anterior 

 portion of the premaxill?e. 



Premaxillse. — Of the premaxillse, the anterior portion has been 

 destroyed, the two posterior teeth on each side only remaining. 

 Since most other forms of plesiosaurs have six teeth on each premax- 

 illa, it is probable that this number was originally present in this 

 specimen, though Andrews gives " but five as the number in Pli- 

 osaurusferox, a related form. Perhaps two-thirds of the dentigerous 

 portion is missing, and I have so restored the outline of the skull 

 (Plate XXXVII). The facial processes are as in the other forms of 

 l^lesiosaurs described by me — elongate, parallel processes, with a dis- 

 tinct longitudinal striation, terminating by overlapping the frontals or 

 parietal processes a little in advance of the anterior end of the orbits. 

 Their width throughout is nearl)^ uniform. They articulate, on the 

 outer side of the skull, with maxillae, frontals and (?) parietals. 



Maxillse. — Each maxilla attains its greatest width over the external 

 nareal opening. It is here separated from the premaxillary process 

 by a slender, pointed projection from the frontal oi* nasal. Between 

 this process and the naris, an elongated tongue-like process extends 

 on the frontal or nasal to a little beyond the posterior end of that 

 opening. Below, the union with the prefrontal begins a little in 

 front of and below the anterior end of the nareal opening and extends 

 downward and backward to the most anterior extremity of the 

 lachrymal. On the right side of the specimen the front part of this 

 suture is apparent,' but in the middle of the course there has been 

 an inward bending on the line of the suture. On the left side, 

 however, the maxilla, while a little displaced, has been separated 

 from its contiguous elements, making certain that the infolding 

 has been at the sutural junction. The maxilla lies somewhat over 

 the prefrontal squamately and helps form only the most anterior 

 part of the nareal opening. The maxillary suture turns backward 

 below the lachrymal to terminate acutely a little before the posterior 

 end of the orbit, joining the jugal posteriorly. 



( ?) Frontals. — The bones wliich I here call the frontals, for reasons 

 given further on, lie at the sides of the parietal prolongations, extend- 

 ing anteriorly as slender projections between the maxillary and pre- 



a Andrews, Quart. Journ. Geol. Soc, LIII, 1897, p. 177, 



