20 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



immediately below the narial border is a deep longitudinal groove for the reception 

 of a slender anterior process from the maxillary, otherwise the union of these two 

 bones is by a straight vertical suture that is strengthened by a vertical median 

 ridge on the posterior end of the premaxillary which fits into a corresponding de- 

 pression on the anterior end of the maxillary. In Antrodemus the premaxillary 

 carries five teeth, all of which, judging from the size of the aveoli and the two teeth 

 preserved in this specimen, are of good size (fig. 10). The second aveolus contains 

 a large worn tooth about to be shed and in the fourth aveolus is a germ tooth the 

 point of which is just beginning to emerge below the dental parapet. Between the 

 five aveolae are four well defined interdental rugosae. A careful comparison of this 

 specimen with the right premaxillary figured by Marsh (on plate 12, fig. 1) Dino- 

 saurs of North America (reproduced here as figure 11), as Creosaurus atrox fails to 

 disclose any important differences, and since Lull has recently written me that this 



bone "mayor may not" belong to the 

 type material, I am inclined to regard 

 it as pertaining to the genus Antrode- 

 mus, and probably also to the present 

 species, though it pertains to a some- 

 what smaller individual than the pre- 

 maxillary described above. The pre- 

 maxillary of Antrodemus is relatively 

 longer than in Ceratosaurus, which 

 carries only three teeth. It may be 

 distinguished from Tyrannosaurus and 

 Coelui'us iOrnitholestes) by the presence 

 of four teeth in the premaxillaries of 

 that genus. The greatest diameter 

 anteroposteriorly of the premaxillary of No. 4734 is 105 mm.; its greatest depth 

 from dental to nasal border is 83 mm. 



MaxiUary (m.). — The left maxillary of No. 4734 is almost entire and in a beau- 

 tiful state of preservation. The functional teeth, with the exception of the ninth 

 from the front, have all been lost. This maxillary contains alveoli for 17 teeth, and 

 Osborn ' has observed in Antrodemus {Allosaurus) , specimens studied by him, that 

 "the maxillaries contain alveoli for from 16 to 18 teeth." 



The type of Ceratosaurus nasicornis has 16 teeth in the maxillary though Marsh 

 says 15 teeth. 



Viewed laterally the maxillary is roughly triangular in outline, heavy in front 

 and slender heliind. Dorsally it sends upward and backward a heavy tapering 

 process that articulates with the nasal and lachrymal. The base of this process is 

 perforated by the second antiorbital fenestra. This fenestra is absent in Cerato- 

 saurus, but is present in Tijrannosaurus. 



The anterior end of the maxillary is abruptly truncated and unites with the 

 premaxillary by an open suture. This end has a transverse thickness of 27 mm. 



FiG.U. — Right PREMAXILLARY OF Antrodemus, sp. Yale mu- 

 seum, i NAT. SIZE. Identified and described by Marsh 

 A3 Creosaurus atrox. a, viewed from front side; 6, 

 viewed from side; c, viewed from internal side. (After 

 Marsh.) 



' Bull. Amer. Mus. Nat. Hist., 1903, vol. 19, p. 700. 



