THE FOSSIL FOOTMARKS OF THE UNITED STATES. 169 



Group I. STRUTHIONIDiE. 



Animal vertebrated, bipedal, tiidactylous, pachjdactjlous. 



Genus I. BRONTOZOUM. 



Foot tridactylous, pachydactylous, tubercular-clawed ; inner toe 

 shortest ; all of them directed forward. Phalangeal expansions on 

 the inner toe, two; on the middle toe, three; on the outer toe, four; 

 corresponding to the number of phalanges, except the distal ex- 

 pansion, which was probably made by the two extreme phalanges. 

 Lower extremity of the tarso-metatarsal bone double-headed ; 

 rarely making a distinct impression through the cushion beneath. 

 Cushion sloping upwards posteriorly. Claws on the lateral toes 

 a little outside of their axes ; on the middle toe, a little towards 

 its inner side. 



Species I. Brontozoum giganteum. (PI. I. Fig. 1.) 



Ornithichnites giganteus, Am. Journal of Science, Vol. XXIX., 

 Plate 1 ; and Buckland's Bridgewater Treatise, Plate 26*. 



Ornithoidichnites giganteus, Final Report on the Geology of 

 Massachusetts, Plate 36, fig. 18. 



Nos. 38-43, 128, 149, 150, 151, of specimens in the Cabinet 

 of Amherst College. 



Divarication of the lateral toes, 40° ; of the inner and mid- 

 dle toes, 20° to 25° ; of the outer and middle toes, 15°. Length 

 of the middle toe, 12.5 inches ; of the inner toe, 10 inches ; 

 of the outer toe, 12.5 inches; of the foot, 14 to 18 inches; 

 of the step, 3 to 6 feet. Width of the toes, 2 to 3 inches ; 

 of the posterior part of the foot, 6.5 inches. Length of the claw, 

 1.75 inch. Distance between the tips of the lateral toes, 12 



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