NO. 9 GRAND CANYON FOSSIL FOOTPRINTS GILMORE 29 



they are so distinct from the other footprints forming the collection 

 from this locality that they seem worthy of description. 



This form is remarkable for the large, heavy, semiquadrate soles 

 and the apparent presence of w^-like flanges that seem to extend 

 between and beyond the tips of the toes. The presence of such a 

 web is indicated in both manus and pes, but more especially the latter, 

 by the depression of the sand between the toes and the numerous 

 cross ridgings marking the surfaces. Its distinct outline is shown in 

 figure I, plate ii. 



The large size of the animal making these tracks is indicated by 

 the size of the footprints and depth of the impressions. Further 

 material will be needed to elucidate the outlines of the feet, and it 

 would not be at all surprising to find that there were additional 

 toes. The web-like character of the feet is also found in the Triassic 

 Otozorum^ but this fact does not necessarily imply any relationship 

 since the great size and dififerent digital formula of the Mesozoic 

 tracks at once distinguishes them. Although subequal in size with 

 tracks here designated AUopus ? arizonae, those of Barypodus palnia- 

 tus are at once distinguished by the long, slender, webbed toes, and 

 by the lengthened quadrate form of the sole impressions. 



A correlation of these tracks with any of the known Permian 

 animals cannot be attempted without additional material, whereby 

 the details of foot structure, length of stride, and width of body 

 could be determined. The largest animals now known from the 

 Permian are Dimetrodon and Edaphosaiirns, either one of which 

 may have been sufficiently large and heavy to make these tracks, 

 but both have five well-developed digits, and it is hardly probable 

 that either had webbed feet. 



ALLOPUS? ARIZONAE, new species 

 Plate II, fig. 2 



Type. — Catalogue nimiber 11,123, U. S. N. 'M. Consists of a 

 consecutive series of footprints 8-J feet in length. 



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

 tional Park, Arizona. 



Geological occurrence. — Coconino sandstone (150 feet above base), 

 Permian. 



Description. — Stride about 530 mm. ; width of trackway about 

 330 mm. Hind foot: Length about 60 mm., width about 85 min. 

 Apparently five toes which are very short with bluntly rounded ex- 



* Hitchcock, Edward, Ichnology of New England, 1858, p. 123, pi. ^3, fig. 4- 



