NO. 9 GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 25 



the digits, and in the proportions and shape of the sole as to fully 

 indicate their generic distinctness. It therefore becomes necessary 

 to erect a new genus for their reception and the name Agostopus 

 mathcri is proposed. The specific name is for Hon. Stephen F. 

 Mather, director of the National Park Service, whose personal inter- 

 est was so largely responsible for the opportunity of making this 

 important collection of fossil footprints. 



The stride is comparatively short for so large an animal and 

 the steps, as well as the width between the right and left rows, are 

 remarkably uniform. The forefoot is placed behind and a little out- 

 side the line of tracks made by the hindfoot. The heel seems to be 

 broadly rounded, as indicated by the broken line shown in figure 16. 

 The heavier outer line of the pes tracks represents the outline of 

 the disturbed sand which was pressed out by the impact of the foot. 

 All of the tracks show distinct imprints of the soles, as may be seen 

 in plate 10. 



Inasmuch as the hindfoot is set partly on the toe marks of the 

 antecedent impression of the forefoot, it resembles Barillopus Mat- 

 thew, but its much larger size, sole longer than digits, different 

 digital formula, and lack of tail mark at once distinguish it from 

 that genus. 



On the forefoot there are apparently five toes, all of which appear 

 to be short. In arriving at the number of digits it was assumed that 

 the divergent projection on the outside of the imprint represents a 

 fifth toe. Such a protuberance is present in several of the tracks 

 though there is a variation in shape and size, as indicated in figure 16. 



Both fore- and hindfeet turn inward toward the center of the line 

 of march. The creature making these tracks was evidently a short- 

 legged, wide-bodied animal, apparently of sluggish habits. 



Genus PALAEOPUS, new genus 



Generic cJiaracters. — Quadrupedal, hindfoot somewhat the larger, 

 always most deeply impressed. Five digits in pes, three or more in 

 manus. Manus in direct line of pes tracks. Sole longer than toes. 

 Broad, short toes without a trace of claws. Feet directed straight 

 forward. Long limbed with regular stride. 



PALAEOPUS REGULARIS, new species 



Plate 5, fig. I 



Type. — Catalogue number 11,143, U. S. N. M. Slab containing 

 a straight series of tracks of a single individual 1,200 millimeters 

 in length. 



