THE FOSSIL FOOTMARKS OF THE UNITED STATES. 197 



Group IV. 



Feet tetradactjlous, plantigrade ; three of the toes directed for- 

 ward, and the fourth situated far back on the heel, making various 

 angles with the axis of the foot. Heel large or long, consisting 

 sometimes of the whole tarsus. 



Gems VII. POLEMARCHUS. 



Heel very large and rounded, making an impression as deep as 

 the toes. Three slender toes directed forward ; the hind toe sit- 

 uated far back on the heel, and at right angles to the axis of the 

 foot. 



Species 1. Polemarchus gigas. (PI. IX. Fig. 1.) 



Sauroidichnites polemarchius, Mass. Geol. Report, Plate So, 

 fig- 17. 



Nos. 34 - SQ, in Cabinet. 



Divarication of the lateral toes, 45° ; of the inner and middle 

 toes, 20° ; of the middle and outer toes, 25° ; of the middle and 

 fourth toes, 80°. Length of the middle toe, 11.2 inches; of the 

 inner toe, 8.5 inches ; of the outer toe, 8.3 inches ; of the hind 

 toe, 2.5 inches ; of the heel, 3.8 inches ; of the middle toe beyond 

 the rest, 3.2 inches ; of the foot, 15 inches ; of the step, 48 inches. 

 Width of the heel, 3.9 inches ; of the foot at the roots of the toes, 

 2.5 inches. Distance between the tips of the lateral toes, &.Q 

 to 8.7 inches ; between the inner and middle toes, 4 to 4.6 inches ; 

 between the middle and outer toes, 5.5 to 7.5 inches ; between 

 the middle and hind toe, 13 inches. Fourth toe straight. Versed 

 sine of the inward curvature of the inner toe, 0.45 inch ; of the in- 

 ward curvature of the middle toe, 0.9 inch ; of the inward curva- 



