38 BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



114: mm. in length. The tooth row is curved slightly in both the vertical and 

 horizontal aspects. The mandibular fossa is present and on the posterior half 

 extends well up between the thin outer wall and the heavier dentigerous part of 

 the dentary. Inferiorly and latterly this fossa is partially inclosed by the splenial 

 which laps along the inner side to a point below the first tooth. Posteriorly the 

 dentary meets the angular and surangular. In all probability, as mentioned pre- 

 viously, it articulates with the prearticular on the postero-internal side. It appears 

 that these elements do not coossify even in old individuals. 



Predentary (pd.). — The predentary has been preserved in situ in the skull of 

 No. 4934 (pd., fig. 1, pi. 9). Although imperfect in some of its details, it never- 

 theless gives a good idea of its chief characteristics and manner of articulation with 

 the dentaries. Viewed from the front it appears as a narrow, transversely curved 

 bone, resting upon the beveled ends of the dentaries. On the median ventral 

 border a narrow pointed process is given off which projects downward and back- 

 ward, being interposed between the ends of the dentaries at the symphysis. 



The predentary is wider transversely than the combined premaxillaries, but does 

 not extend so far forward as those bones. (See pd., pi. 8.) The median anterior sur- 

 face is somewhat flattened and with the forward ends of the dentaries forms the 

 rather truncated end of the mandible. This surface of the predentary is pitted by 

 numerous but irregularly placed pits. In life this bone was probably enveloped 

 by a horny covering and when in contact with the premaxillaries similarly covered 

 must have served as an efficient organ for gathering the plants upon which the 

 animal fed. 



Splenial (s.). — The splenials are long, thin bones that are closely applied to 

 the internal side of the dentary (s., pi. 8). They reach a point 60 mm. posterior to 

 the symphysial border in front, and posteriorly they inclose internally and inferiorly 

 the mandibular fossa. Posteriorly they extend back to a point 83 mm. from the 

 end of the ramus and lap along the angular and prearticular. Below the junction 

 of the dentary and angular on the infero-lateral border the splenial is visible for a 

 short distance from a lateral view (s., pi. 5). 



Angular (an.).— The angular is also a long, thin element, which forms the outer 

 and lower part of the posterior portion of the ramus. Dorsally it unites with the 

 surangular by a nearly horizontal suture. In specimen No. 4934, however, as 

 shown in plate 5, the anterior half of this suture has been entirely obliterated and 

 the union of the angular, surangular, and dentary is obscure. 



The anterior end appears to be overlapped by the dentary on the outside and 

 by the splenial on the inside. Posterior to the end of the splenial the ventral 

 border of the angular is swollen transversely and underlaps for a short distance 

 the ventral border of the prearticular (see pi. 7), but more posteriorly it returns 

 to the external side of the articular terminating in a sharp end somewhat anterior 

 to the posterior termination of the surangular. 



Surangular (sa.). — The surangular is a comparatively thin, flat bone, and the 

 largest of the posterior elements of the jaw. Ventrally it sends forward a thin 

 tapering extension which laps along the outside of the dentary. Posteriorly the 

 surangular forms the upper border of the posterior one-third of the ramus. Near 



