THE FOSSIL FOOTMARKS OF THE UNITED STATES. 203 



that the species of Tricenopus may be quadrupeds, or rather that 

 there is but one species of this genus, and that a quadruped, with 

 feet quite unlike. For, in several cases, I find two tracks occupying 

 almost exactly the same place, and pointing in the same direction, as 

 has been shown in the case of Plectropus longipes. But the tracks 

 of Tricenopus are extremely crowded together ; and although more 

 perfect than any others I have ever found, yet I have not been able 

 to trace out consecutive tracks. So brittle is the beautiful red shale 

 on which they are imprinted, that it is rare to be able to obtain 

 specimens more than a foot square. 



Species 1. Tricenopus Baileyanus. (PI. X, Fig. 4.) 



Sauroidichnites Baileyi, Mass. Geol. Report, Plate 32, figs. 8, 9. 



Nos. 13-16, 161, 162, 165, 166, 168, 169, 175, 178, 179, 212, 

 in Cabinet. 



Divarication of the lateral toes, 35° to 40° ; of the inner and 

 middle toes, 15° to 20° ; of the middle and outer toes, 15^" to 20° ; 

 of the middle and hind toe, 30° to 40°. Length of the middle toe, 

 2.5 to 3.3 inches ; of the inner toe, 1 .6 to 2.2 inches ; of the outer 

 toe, 2 to 2.5 inches ; of the hind toe, 0.7 to 0.9 inch ; of the heel, 

 1.4 to 2 inches ; of the foot, 4 to 4.9 inches ; of the step, 7 inch- 

 es (?) ; of the middle toe beyond the rest, 1,5 inch. Distance be- 

 tween the roots of the forward toes and that of the hind toe, about 

 1 inch; between the tips of the lateral toes, 1 to 1.8 inch ; between 

 the inner and middle toes, 1.1 to 1.6 inch ; between the outer and 

 middle toes, 1.3 to 1.7 inch ; between the middle and hind toe, 3.2 

 to 3.7 inches. Extremity of the heel adhering to the mud, so that 

 when the former was lifted up, the latter followed, forming a ridge. 

 Behind this ridge we sometimes find what seems a continuation of 

 the heel backward ; or, more probably, a hind toe, sometimes more 



