118 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



in their final conclusions through the inaccuracy of the fore limb and foot assigned 

 to Antrodemus by Marsh. Fortunately the true structure of the Antrodemus fore 

 limb is now known/ and differences which the above authors were unable to reconcile 

 now disappear. Both Williston and Hay were of the opinion that Creosaurus atrox, 

 type species of the genus, was based chiefly if not entirely on the left ilium. In 

 reply to my inquiry as to the material in the Yale Museum comprising the type 

 specimen of C. atrox Marsh., Prof. R. S. Lull, very kindly wrote me under date of 

 April 14, 1916, as follows: 



Skull-jugal and premaxillary containing teeth, ? hyoid: two sacral vertebrae without the neural 

 arches, a proximal caudal without neural arch, and a small distal caudal. Apparently the caudal (lum- 

 bar) figured by Marsh does not belong to the original type specimen and its characteristics are some- 

 what different. There is, in addition, a sternal bone, an ilium complete, an astragalus with two and 

 a half proximal phalanges of the foot, and two unguals, one a powerful grasping claw. 



Hay, 2 after a careful and detailed comparison of the published figure of the 

 Creosaurus ilium, with the ilium of No. 4734, U.S.N.M., says: 



Whatever may be true of other parts of the skeleton of Creosaurus, there do not appear to be any 

 characters in the ilium that distinguish it generically from Allosaurus. 



The premaxillary carries five teeth, as in Antrodemus. When the figures of 

 this bone as given by Marsh are compared with the actual specimen in Antrodemus, 

 No. 4734, U.S.N.M. (see figs. 10 and 11), its proportions and chief characteristics 

 are found to be identical. 



Williston 's 3 summing up of the few characters given for Creosaurus by Marsh 

 is as follows : 



The ilium, it is true, is of somewhat different shape, as figured, but even this difference may be due 

 to imperfect preservation, as Marsh himself suspected. The only other things mentioned by Marsh are 

 the number of vertebrae (two) in the sacrum, of very little value as already demonstrated in other genera 

 of the Wealden dinosaurs; the position of the transverse processes, which I am confident will not prove 

 distinctive. 



Hay also states in the publication cited above : 



The metapodial whose measurement was given by Marsh has the same length relative to the length 

 of the ilium that the fourth metapodial of Allosaurus Jragilis has to its ilium, being about 40 per cent. 



From the above review it will be observed that none of the more important 

 bones constituting the type specimen of Creosaurus atrox show generic differences 

 from Antrodemus, and I believe therefore that the genus should be abandoned, to 

 become a synonym of Antrodemus. As to the validity of the species A. atrox, a care- 

 ful study of the specimen itself will be necessary before a decision can be reached, 

 and that is a question outside the scope of the present study. 



While the brief review of Creosaurus, given above, seems to indicate its being 

 a synonym of Antrodemus, a comparison of the type of Creosaurus potens Lull 

 with an anterior caudal of Antrodemus (see pi. 32, figs. 1 and 2) shows such dis- 

 similarities as to render its assignment to that genus out of the question. Further- 

 more, none of the known Morrison Theropod genera have the straight inferior 

 profile of the anterior caudals as seen in this Arundel specimen. 



i Gilmore, Charles W., Proc. XJ. S. Nat. Mus., vol. 49, 1915, pp. 501-513. 



2 Proc. U. S. Nat. Mus., vol. 35, 1898, p. 355. 



3 Amer. Journ. Sci., vol. 11, 1901, p. 112. 



