120 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



The type tooth has been carefully compared with teeth of Antrodemus and 

 Oeratosaurus, and with those of Upper Cretaceous Theropods; but I have failed to find 

 characters that would distinguish it from any of those genera. In fact on the basis of 

 a single tooth I believe it is impossible to determine the genus to which it pertains, 

 and certainly there are not diagnostic characters available for generic or specific 

 differentiation. In so far as the type specimen is concerned it will always remain a 

 form of doubtful affinities. For the present, however, it would seem best to con- 

 tinue the use of the species in order to have a name for those scanty Theropod 

 remains that are found from time to time in the Arundel formation. The generic 

 assignment is seriously in doubt, and I here provisionally refer it to the genus 

 Dryptosaurus, largely on geographic considerations. A more definite conclusion must 

 await the discovery of better and more diagnostic materials. 



In his paper on the vertebrata of theLowerCretaceousof Maryland, Lull iden- 

 tified and described a number of separate bones as belonging to this species. All 

 of these specimens are now deposited in the United States National Museum and in 

 order to assemble here all available information relating to Dryptosaurus? medius, 

 Lull's remarks are given in full as follows: 



There are several larger, better preserved teeth' among the material, one of which (No. 5685, 

 Goucher College)- shows decided wear. The most perfect is one in possession of the Hon. Charles E. 

 Coffin, Muirkirk, Maryland, [pi. 34, fig. 1]. It is about 3 inches (7() mm.) in length and IJ inches 

 (28.7 mm.) in the antero-posterior diameter. The crenulations of the margin cease about midway 

 toward the root on the anterior convex border, but extend the length of the crown on the posterior edge. 

 There is a slight variation in the size of the crenulations as they are somewhat coarser in the larger teeth. 



The two vertel^rae which are here referred to this species indicate an animal of the same approximate 

 size as the teeth and phalanges. One (No. 2534, G. C.)^ which seems to be a posterior presacral has a 

 form quite similar to the type of Altosaurus fra-jilis, but relatively somewhat less constricted in the 

 middle. It agrees in having the same somewhat flattened inferior surface. Anteriorly, the centrum 

 has a shallow concavity, while posteriorly it is nearly plane. The pedicels of the neural arch are stout, 

 and the neural canal seems to be broader than in the type of A.fragilis, possibly owing to the fact that 

 the vertebra is a more posterior one. The two agree in the depression on either side, which however, 

 is somewhat less marked in the present species. 



Dimensions. 



mm. 



Length : 90. 



Least diameter of centrum 68. 5 



Diameter of anterior face as preserved 105. 



Diameter of posterior face as preserved 95. 5 



Heigh th of centrum 85. 



The anterior caudal vertebra (No. 2614, a, G. C.)* is that of a young individual, as the neural arch 

 had not coossified with the centrum. Internally it seems to have been composed of rather coarse, 

 cancellous tissue, with no trace of an internal cavitj , as in the type of Antrodemus, as figured by Leidy .^ 



The anterior face is slightly concave, the posterior one nearly plane, and while the centrum is 

 decidedly constricted in the middle there is no trace of the lateral depressions seen in the presacrals. 



> Other teeth in the V. S. National Museum Collections are Nos. .5693, 3446. and 8447. 



- Wrongly attributed to Goucher College as this is the Catalogue number of the XJ. S. National Museum. 



3 Now Cat. No. 8502 U.S.N. M. 



* I regard this vertebra as being the anterior vertebra of the sacral series and the plane end (which appears to be sutural) as 

 being posterior. That it is a sacral is indicated not only by comparison with the articulated sacral series of No. 4734 U.S.N.M. 

 (.AntTodemus valens), but also by the character of the plane articular end for close articulation with the centrum which followed 

 it and the rapid widening of the anterior half of the neural canal. 



s Now Cat. No. 8303, U.S.N.M. 



5 Leidy, Report of U. S. Geological Survey of Tennessee, vol. 1, 1873, pi. 15, fig. IS. 



