NO. 3 GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 29 



the single known species, A. mathcri, it is to be distinguished by its 

 larger size, the relatively wider soles, and the short, stout form of 

 digit IV. 



Genus AMBLYOPUS, new genus 



Generic characters. — Quadrupedal, plantigrade. Toes of both 

 manus and pes not differentiated but inclosed in the foot mass. Im- 

 pressions of feet reniform in outline, being longer than wide. Pes 

 tracks placed partly upon those of manus, and forming rows inside 

 them. 



Genotype. — Auihlyopus pacJiypodiis, new species. 



AMBLYOPUS PACHYPODUS. new species 

 Plate 9 



Type. — Catalogue number 11,511, U. S. N. M. Consists of a slab 

 830 mm. long, having a trackway running the entire length. 



Type locality. — Hermit Trail, Hermit Basin, Grand Canyon Na- 

 tional Park, Arizona. 



Geological occurrence. — Coconino sandstone (about 130 feet above 

 bas6), Permian. 



Description. — Stride about 210 mm. ; width of trackway about 

 330 mm. Hindfoot placed partly upon the imprint made by the fore- 

 foot. Hindfoot: Length about 100 mm. None of the footprints, and 

 most of them are well impressed, gives any indication of the presence 

 of separate toes, but in the deepest part of the pes tracks two longi- 

 tudinal parallel tapering depressions (see fig. 12) evidently indicate 

 the presence of at least two digits, but these were wholly inclosed 

 within the mass of the foot. It is this peculiarity that has suggested 

 the specific name pachypodus. The anterior portion of the imprints 

 gives the impression of their having been made by a single broad toe, 

 which had a broadly rounded ungual. This end measures 53 mm. in 

 transverse diameter. On the inner side and a little jjosterior to its 

 midlength a pronounced indentation may represent the division be- 

 tween toes and sole. The outline of the hindfoot impression as a 

 whole ma}' be said to be reniform. The sole is subquadrate in outline 

 and well impressed in nearly all of the tracks, especially the series 

 of the right side. Forefoot: The ])lacing of the hindfoot wholly or 

 in part upon the impression made by the forefoot has obliterated most 

 of the details of its structure. It is quite evident that the feet were of 

 about equal size, and from what little can be seen of them, that there 

 was a similarity of structure. These resemblances are clearly shown 



