PROCEEDINGS OF THE NATIONAL MUSEUM 



Tlie series of tracks selected as being typical of the above-named 

 species is shown on the lower two thirds of the slab illustrated in Plate 

 1. With the exception of four faint impressions shown on the bottom 

 of Plate 2, all other tracks on the three slabs illustrated in Plates 

 1, 2, and 3 are regarded as pertaining to the present genus and species. 



Description.. — Stride vari- 

 able, measuring from 135 

 to 180 mm. ; width of track- 

 way measured from the out- 

 side of one foot to a cor- 

 responding position on the 

 opposite side, about 162 mm. 

 The manus tracks irregu- 

 larl}^ placed but usually for- 

 ward of midway between 

 those made by the hind feet. 

 Fore slightly smaller than 

 hind foot. 



Mayiws. — Tetradactyle, 

 plantigrade, rounded palm, 

 and diverging digits. 

 Length over all, 22 mm. ; 

 distance between tips of lat- 

 eral toes 31 mm. ; breadth of 

 palm, 20 mm. Outer toe 

 originates well backward on 

 the side of the palm and is 

 strongly diverted outward 

 away from the three inner 

 toes. The manus as a 

 whole turns strongly inward 

 toward the median line of 

 the trackway. Inner toe 

 shorter than fourth digit. 

 Third longest. 



Pes. — Pentadactyle, plan- 

 tigrade. Sole broadly 

 rounded behind. Length over all, 33 mm.; distance between tips of 

 lateral toes, 33.5 mm. ; breadth of sole, about 28 mm. First digit short 

 and originating well back on the side of the sole; divercation slightly 

 less than 45°. Three median toes long, relativelj'^ slender, Avith sub- 

 racute or rounded terminations. There is some variation in the rela- 

 tive lengths of the digits of opposite feet as is clearlj^ indicated in 

 Figure 1. None of the tracks give clear indication of the presence of 



Fig. 1. — Ammobatkachis montanexsis. Type No. 

 7635 U. S. N. M. Diagram of Trackway. 

 About One-third Natural Size 



