OSTEOLOGY OF CARNIVOROUS DINOSAURS. 121 



Dimensions. 



mm. 



Length 107 



Least diameter 59 



Diameter anterior face 101 



Diameter posterior face 93 



Height of centrum 92 



The first phalanx of the second digit is represented by the proximal half (No. 2536, G. C.),' and is 

 peculiar for its height as compared with its width and the two very prominent ridges on the inferior face. 

 The articulation is a smooth cylindrical concavity with no trace of ridges to limit lateral motion. It is 

 probable that it was formerly somewhat cuplike, as the preparator has slightly altered the shape of the 

 bone. The articular end is full of a cancellous tissue, nevertheless there was a weH-defined medullary 

 cavity in the shaft. The portion preserved measures in height 73 mm. ; in width 58 mm. 



The first phalanx of the third digit (No. 2521, G. C.) 2 (fig. 2) [pi. 34, fig. 3] is entire, most excellently 

 preserved, and presents a decided similarity to the type of Allosaurus fragilis, differing therefrom in 

 being more depressed proximally, especially in the broader, flatter under surface. Distally, the present 

 type is not so broad relatively as that of A. fragilis and the articular face is more concave transversely. 

 Altogether the two bones are quite distinct in conformation. 



Dimensions. 



mm. 



Length .' 110. 



Transverse diameter distal face 55. 



Vertical diameter distal face 35. 5 



Transverse diameter proximal face 70. 5 



Vertical diameter proximal face 50. 



Least transverse diameter, shaft - 41. 



"All of the remains which Lull referred to Allosaurus medius are from the Arundel 

 formation in the vicinity of Muirkirk, Prince Georges County, Maryland. 



The two distal caudal vertebrae described by Lull in the article quoted above 

 undoubtedly pertain to an Ornithomimid dinosaur and are here referred to the new 

 species Omithomimus affinis (see p. 141). 



While there may be two large carnivorous dinosaurs (Dryptosaurus? potens 

 (Lull) and D. medius (Marsh) present in the Arundel fauna, I can see no good 

 reason at the present time for believing there is more than one, even though, as a 

 matter of expediency, both species are retained in the present paper. Certainly 

 the scattered teeth and other bones assigned to D. medius indicate an individual or 

 individuals of sufficient size to have had an anterior caudal of the dimensions of 

 the type of Creosaurus -potens, here referred to the genus Dryptosaurus. 



TYRANNOSAURUS REX Osborn, 1905. 



Tyrannosaurus rex Osborn, Bull. Amer. Mus. Nat. Hist., vol. 21, pp. 262-263; vol. 22, pp. 281-296, 

 1906; Mem. Amer. Mus. Nat. Hist., vol. 1, pt. 1, pp. 3-30, 1912, pis. 1-4, 27 text figures; Bull. 

 Amer. Mus. Nat. Hist., vol. 32, pp. 91-92, 1913; vol. 35, pp. 761-771, 1917. 



Omithomimus grandis Marsh, O. C, Sixteenth Ann. Rept., IT. S. Geol. Surv., pt. 1, 1896, p. 206. 

 (Not O. grandis of 1890.) 



In the United States National Museum collection there are a number of isolated 

 bones which are here regarded as pertaining to the genus Tyrannosaurus, and in all 

 probability to the species T. rex Osborn. 



i Now Cat. No. 8504, U.S.N.M. This bone belongs to the right hind foot. 



2 When the Goucher College collection was deposited in the TJ. S. National Museum this specimen was missing. 



