144 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



tion of the distal portion. This distal end is slightly grooved- — -a feature that is 

 not found in the other species of the genus. The bone is hollow and with thin 

 walls. The inner side is flattened all along the shaft for contact with metatarsal 

 III. It measures 32 mm. in length; a greatest transverse diameter of the distal 

 end of 5 mm., and a greatest fore and aft diameter of 4 mm. 



The phalangials consist of the distal halves only. Their slightly expanded 

 articular ends are grooved, the grooves and the rounded articular ridges on either 

 side extending far up on the back of the bone. There are pronounced lateral pits 

 on the sides, as in the larger species of the genus. 



"CARNIVOROUS DINOSAURIAN" Cope. 



Carnivorous Dinosaurian Cope, E. D., Rept. U. S. Geol. Surv. W. 100th Merid., vol. 4, pt. 2, p. 

 28, 1877, pi. 22, fig. 15.— Merrill, G. P., Bull. No. 53, pt. 2, U. S. National Museum, 1907, 

 p. 65. 



Specimen.— No. 2592, U.S.N.M. Consists of a single tooth. 



Locality. — Gallinas Creek, New Mexico. 



Horizon. — Triassic. 



The above specimen Cope regarded as the tooth of a Theropod dinosaur of 

 "the general character of Laelaps" ; does not pertain to the dinosauria, at all, 

 but to the Crocodylia to the family Phytosauridae. 



OBSERVATIONS ON THE PROGRESSIVE STRUCTURAL MODIFICATIONS OF THE 



THEROPOD SKELETON. 



In the course of this detailed study and comparison of the Antrodemus and 

 Ceratosaurus skeletons with Theropod specimens from other geological formations, 

 certain modifications were observed which appear to me to represent some of the 

 progressive structural changes that the Theropod skeleton has undergone during 

 successive geological periods. 



Geologically the Theropoda have the greatest range of all the dinosaurs and 

 should therefore furnish the most complete story of their development and speciali- 

 zation, but unfortunately many of the described genera and species have been 

 founded on such scanty materials that our knowledge of the complete structure 

 is too inadequate on which to make deductions or draw conclusions. 



The work of recent years, however, is gradually correcting this condition 

 through the recovery of more perfect skeletons, and it may be predicted with some 

 degree of assurance that before many decades have passed our knowledge of the 

 structural changes in the Theropod dinosaur skeleton will enable a paleontologist 

 to determine from the stage of development its proper position in the geological 

 column although this knowledge will probably never reach the degree of refinement 

 attained in the mammalian structures. 



Osborn 1 was the first among American paleontologists to call attention to some 

 of the progressive changes in the development of the Theropod skull. The more 

 important of these, relating especially to members of the Megalosauridae, may be 

 summarized as follows : 



1 Osborn, Henry F. Mem. Amer. Mus. Nat. Hist., vol. 1, pt. 1, 1912, p. 29. 



