584 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



remain a form of doubtful affinities. It is determinable as to sub- 

 order (the Theropoda), but in the present state of our knowledge 

 concerning the carnivorous dinosauria it is not determinable generi- 

 cally, and should therefore be regarded as an indeterminate type. 



The few scattered bones referred to this species by Lull can be 

 assigned, with equal propriety, to Dryptosaurus? potens Lull, founded 

 on a somewhat more adequate type. I have already, in the paper 

 cited above, attempted to show that two caudal vertebrae, from the 

 distal part of the tail formerly referred to this species, probably 

 pertain to an Ornithomimid dinosaur, and some of the other bones 

 may eventually find a similar fate in other directions. 



It is quite probable that these scattered elements represent more 

 than one kind of the large carnivorous dinosauria in this formation, 

 but to definitely determine that fact more diagnostic materials must 

 necessarily be found. 



DRYPTOSAURUS ? POTENS (Lull). 



Plate 111, fig. 2. 



This species was originally referred by Lull 11 to the genus Creosaurus, 

 a genus established by Marsh on materials from the Morrison forma- 

 tion of Wyoming. In a recent paper 12 giving the results of a detailed 

 study and comparison of the type with other Theropod specimens 

 I arrived at the following conclusions: 



1. That the genus Creosaurus should be abandoned to become a 

 synonym of Antrodemus. 



2. That the type specimen, consisting of a single vertebral centrum 

 (see pi. 1 1 1 , fig. 2) , pertains to the caudal series and not to the presacral 

 region as originally determined. 



3. That a comparison of the type specimen with the homologous 

 element in Antrodemus (compare figs. 1 and 2, pi. Ill), shows such 

 dissimilarities as to render its assignment to that genus out of the 

 question. 



4. That the closest resemblance of the type vertebral centrum 

 appears to be with the caudals of Dryptosaurus aquilunguis Cope 

 (compare fig. 2, pi. Ill, with fig. 2, pi. 114), and it was therefore provi- 

 sionally referred to that genus. 



When viewed in profile the straightness of the ventral border with 

 distinct keel at once distinguishes this bone from all known carni- 

 vorous dinosaurs of the Morrison formation. In Tyrannosaurus and 

 Gorgosaurus from the western Upper Cretaceous the concavity of the 

 lower border of the anterior caudal vertebrae is markedly straighter 

 than in any of the Morrison Theropods, and in Dryptosawus as 

 figured by Cope (see pi. 114, fig. 2), from the Upper Cretaceous of 



> l Lower Cretaceous of Maryland, Maryland Geol. Survey, 1911, pp. 186-187, pi. 14, fig. 4. 

 u Bull. 110, U. S. National Museum, 1920, pp. 116-119, pi. 32. 



