70 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



dian toes, although directed straight ahead in the direction of move- 

 ment, have a tendency to turn outward. The sole of the foot is 

 relatively narrow and supplied with palmar pads. The toes have the 

 following lengths: 1 = 5 mm.; II = 35 mm.; Ill = 35 mm.; IV = 

 26 mm. Hindfoot placed in front of forefoot and the impression of 

 the sole usually obliterating the toes of the forefoot. Forefoot: Length 

 about 68 mm. ; width measured from tip of digit I to tip of digit III, 

 53 mm. Three digits. Outer toe stout, with broadly rounded ex- 

 tremity and spreading outward from the others. Digit I and II as 

 in the pes, long, comparatively slender, parallel acuminate and di- 

 rected straight forward. Sole relatively narrow with broadly rounded 

 heel. Length of toes as follows: I = 29 mm. ; II = 27 mm. ; III = 

 18 mm. 



This series of footprints is impressed on a fine grained pinkish 

 colored sandstone that is covered with worm trails. The footprints 

 are deeply impressed and clearly defined except that portions of the 

 forefoot track are destroyed by the hindfoot partially stepping 

 upon it. 



The species is named for Mr. Glen E. Sturdevant, ranger natu- 

 ralist of the Grand Canyon National Park, who discovered and col- 

 lected the specimen, and through whose efforts it was presented by 

 the Park Service to the United States National Museum. 



Genus TRIDENTICHNUS, new genus 



Generic cJiaractcrs. — Quadrupedal, semiplantigrade. Five toes in 

 pes, three ? in manus. Manus smaller than pes, with hindfoot placed 

 behind forefoot. 



Genotype. — Tridcntichnns supaiensis, new species. 



TRIDENTICHNUS SUPAIENSIS, new species 

 Plate 21 



Type. — Catalogue number 11,534, U. S. N. M. Consists of a slab 

 on which is a trackway of eight imprints divided equally between the 

 feet of the two sides. 



Type locality. — -Hermit Gorge (to the left of Hermit Trail, de- 

 scending, about one-half mile below Santa Maria Spring), Grand 

 Canyon National Park, Arizona. 



Geological occurrence. — Supai formation (upper track bearing 

 horizon; about 350 feet below top), Pennsylvanian. 



Description. — Stride about 185 mm., width of trackway about 

 187 mm. Forefoot placed about 18 mm. in front of hindfoot; in 



