8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ']'] 



of Drouwpus agilis Marsh, such as the long, curved fourth digit 

 with curved claw, as shown in figure 3. The absence of a fifth toe 

 on the outside of the foot, the reversed curvature of the digits, 

 and the hindfoot impression behind the fore show, however, that 

 the two sets of tracks were made by quite different animals. 



The footprints of Dolichopodus tetradactylus appear to have been 

 made by an active animal with long hind limbs and a comparatively 

 light body. That this creature carried the greater part of its weight 

 almost entirely upon the hind limbs seems to be shown by the great 

 depth of the imprints made by the hindfeet. 



Fig. 3. — Dromopus agilis Marsh. Diagram of left fore and hind 

 footprints. \ natural size. (After Marsh.) 



A survey of the known vertebrate fauna of the Permian discloses 

 only one form, Araeoscelis, which, in its structure, is suggestive of 

 a type of animal that might make a trackway similar to the foot- 

 prints under consideration. Perusal of Williston's osteological de- 

 scription shows that a complete pes of this animal is unknown, but 

 the restoration (see fig. 4) shows a fifth digit. In commenting on 

 the number of digits Williston says : ^ 



Only four metatarsals are preserved together in any one specimen, though 

 the presence of the first tarsal would seem definitely to indicate the presence 

 of the full five. 



It would seem, therefore, that Araeoscelis must be ruled out of con- 

 sideration as the maker of these tracks. On the other hand, the lack 

 of evidence of a fifth toe in the tracks may be due to its failure to 



^ Williston, S. W., Journ. Geo!., Vol. 22, 1914, p. 390. 



