30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ""J 



tremities without claws. Third toe broadest. Two outer toes sHghtly 

 diverted from three inner as in Allopus litforalis Marsh. Sole im- 

 pressed but its posterior outline obscure ; it appears to have been 

 broadly rounded as in Allopus. Foot turned strongly inward toward 

 the line of movement. Forefoot: Length (estimated) 45 mm., width 

 about 22 mm. Two toes clearly recorded, but there may have been 

 one or two more. Digital terminations especially broad and without 

 claws. Sole appears to be broadly rounded behind. Footprint deeply 

 impressed on the inside, angle ot inclination inward toward the lino 

 of movement and less than the hindfoot. 



The specimen selected as the type of this new species is the track- 

 way of a quadruped and consists of eight pairs of footprints equally 

 divided between the right and left sides. In size, length of stride, 



Fig. 19. — Allopus f arizonae. Type, No. 11,123, U. S N. M. 

 Sketch of left hindfoot. About i natural size. 



and toes with blunt, rounded extremities without claws, these show 

 a marked resemblance to Allopus Hit oralis Marsh ^ from the Coal 

 Measures of Kansas. I shall, therefore, tentatively refer these tracks 

 to the genus Allopus, although there are differences which suggest 

 that they probably pertain to a distinct genus. 



The tracks are deeply impressed, but the sand was apparently so 

 soft that the detailed foot plan was not recorded. Furthermore, the 

 trail is crossed diagonally by the trackway of a second large animal, 

 apparently of the same species, which in several instances stepped 

 upon the footprints of the first, thus contributing still further to 

 the difficulty of their proper interpretation. The last three pairs of 

 the left side are the most distinct and the description is based almost 

 entirely upon these six impressions of the fore- and hindfeet. 



The consecutive series of tracks is unique from the fact that this 

 was the only trackway found at this locality leading down the in- 

 clined slope ; all others were ascending. For that reason there is 



^ Marsh, O. C. Amer. Journ. Sci., Vol. 48, 1894. p. 8.3, pi. 11, figs. 4, 4a. 



