OSTEOLOGY OF CARNIVOROUS DINOSAURS. 6 



During the half century that has elapsed since Antrodemus was established, 

 it will be observed from the above review, but little attention has been given this 

 genus, due, no doubt, to the scanty materials on which it was founded. 



Recently I have made a very careful comparison of the type specimen of Antro- 

 demus valens with the anterior caudal vertebrae of No. 8367 U.S.N.M., a specimen 

 previously identified as Allosaurus fragilis Marsh, and such close resemblances were 

 found as to indicate their generic identity. 



In plate 1, figures 1 to 6, is shown, in three aspects, comparative views of the 

 genotype of Antrodemus with a caudal of corresponding size of the above specimen. 

 Their close resemblance down to the minutest details is clearly indicated. Their 

 comparative measurements are as follows: 



Greatest vertical diameter of posterior end of centrum 



Greatest transverse diameter of same 



Length of centrum 



Least transverse diameter of centrum at center 



Type of 



Antrodemus 



valens 



No. 218, 



U.S.N.M. 



No. 83«7, 



U.S.N.M., 



'sixth caudal. 



mm. 

 102 



mm. 



104 



99 



100 



el25 



125 



56 



49 



« Estimated. 



The medullary cavities within the body of the centrum are larger in the genotype 

 than in No. 8367, but this may be due to a slight difference in the position of the 

 point where the cross section was taken. At most it is only a difference of degree 

 and certainly does not indicate any important structural modification. 



Unfortunately direct comparison can not be made with the genotype of 

 Allosaurus, inasmuch as no anterior caudals are preserved with that specimen. The 

 so-called caudal mentioned in Marsh's original description, below, turns out to be 

 the damaged centrum of a dorsal vertebra. See plate 2, fig. 2. 



The original description 1 of Allosaurus fragilis Marsh consists of the following : 



This genus may be distinguished from any known Dinosaurs by the vertebrae which are peculiarly 

 modified to insure lightness. Although apparently not pneumatic, they have the weight of the centra 

 greatly reduced by deep excavations in the sides. Some of them have the centra hourglass in form, 

 the middle part being so diminished as to greatly reduce the strength. The vertebrae preserved are 

 biconcave, with shallow cavities. The feet bones referred to this species are very slender. A lumbar 

 vertebra has its centrum 105 mm. in length, and 89 mm. in least transverse diameter. An anterior 

 caudal, 85 mm. long, has its centrum so much constricted that its least transverse diameter is 38 mm., 

 while its anterior face is 90 mm. in transverse diameter. 



The animal indicated by the remains preserved was from 15 to 20 feet in length. All the known 

 specimens are from the upper Jurassic of Colorado. 



The type of Allosaurus fragilis Marsh is in the Peabody Museum of Yale Univer- 

 sity, and in a recent letter Professor Lull informs me it is from "Garden Park," 

 near Canon City, Fremont County, Colorado, collected by B. F. Mudge in 1877. 

 It bears the catalogue number 1930 of the Yale Museum. The type material is 



i Marsh, O. C, Amer. Journ. Sci., vol. 45, 1877, pp. 5U-516. 



