26 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Supradentary (s. d.). — The supradentary is missing from this specimen No. 

 8335, U.S.N.M. That such an element was present is obvious after a comparison 

 with the more perfect ramus of Ceratosaurus nasicornis. The bone mentioned by 

 Osborn 1 as the "presplenial" in his preliminary description of the Antrodemus 

 (Creosaurus) jaw is in all probability the supradentary plate. He says: "If this 

 is truly the presplenial it appears to extend as far forward as the symphysis. " This 

 is the condition in Ceratosaurus (fig. 55 d. p.). 



Splenial (s.). — The complete splenial bone is apparently unknown in Antrode- 

 mus. It is missing in all of the specimens before me, but from the little available 

 evidence it appears to have been a thin, triangular-shaped bone, that overlapped 

 the inner side of the dentary, extending anteriorly for about half its length. 



Coronoid (c). — The coronoid is also missing from the specimens before me. 

 Osborn in the article cited above says: "The suture between the coronoid and 

 angular is faintly determinable posteriorly, the coronoid being depressed." Evi- 

 dently the suture mentioned was that between the coronoid and the surangular. In 

 the restoration of the ramus the coronoid was restored to fill the small triangular 

 space between the prearticular and surangular as in Tyrannosaurus. 2 



Angular (an.). — The complete angular in Antrodemus is unknown. In figure 2, 

 on plate 4, this bone has been restored after that element in Ceratosaurus. Its 

 posterior extent appears to be indicated on the external side of the surangular and 

 prearticular by a smoother surface and this peculiarity guided us somewhat in 

 restoring this bone. 



Surangular {sur. and sa.). — With specimen No. 4734, U.S.N.M., was found the 

 nearly complete posterior portion of the right ramus in a beautiful state of preserva- 

 tion. 



For the first time a complete surangular, articular, and prearticular are now 

 known of Antrodemus. Unfortunately several of the sutures have become obliterated 

 through coossification and the exact extent of certain parts of these bones can not 

 be absolutely determined. 



This specimen shows the surangular to have a very extensive exposure on the 

 external side, which forms the entire upper border of the posterior half of the jaw. 

 It is a relatively long bone, as in Ceratosaurus, and overlaps the posterior end of the 

 dentary by a long squamous union. The bone is thin with the exception of the dorsal 

 portion which turns inward at nearly right angles to the lateral surfaces and is 

 somewhat thickened. Anteriorly, this inner extension has a longitudinal groove 

 for the articulation with the upper posterior part of the dentary (C, fig. 15). Pos- 

 teriorly, it articulates with the articular, and with that bone forms the outer part 

 of the cotylus for articulation with the quadrate. It continues backward along the 

 outer side of the articular but stops slightly forward of its posterior extremity. 

 Ventrally it is suturally united with the angular and prearticular as indicated in 

 figure 15. 



On the median ventral border it is deeply notched by the external mandibular 

 foramen, shown in figure 15 (A) ex. f. 



The small posterior foramen observed in the surangular of Tyrannosaurus rex 

 Osborn and Gorgosaurus libratus Lambe is not present in Antrodemus, though on the 



1 Bull. Amer. Mus. Nat. Hist., 1903, vol. 19, p. 701. * Mom. Amer. Mus. Nat. Hist., new ser., vol. 1, pt. 1, p. 22, fig. 18. Cot. 



