NO. 3 



GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 



71 



one pair of tracks slightly outside of it. Forefoot smaller than hind- 

 foot. Hindfoot: Length about 68 mm., width about 70 mm., five 

 toes, the three median ones subequal in length and directed forward ; 

 first much shortened and extending forward and inward, while the 

 fifth is widely set ofT from the others and is directed almost straight 



Fig. 37. — Tridentichnus supaiensis. Type. No. 11, 534. U. S. N. M. 

 Diagram of a portion of trackway. About 3 natural size. 



outward. Three median toes bltnitly acuminate, second and fourth hav- 

 ing a tendency to turn in toward the third (see fig. 37). Sole broader 

 than long and broadly rounded behind. Digits have the following 

 lengths: I = 10 mm. ; II = 23 mm. ; III = 26 mm. ; IV = 26 mm. ; 

 V =: 13 mm. Forefoot: Length (estimated) about 40 mm., width of 

 three toes 48 mm. Three toes impressed, but there may have been more 

 in the complete complement. The three tnedian toes bear a strikingly 



