THE FOSSIL FOOTMARKS OF THE UNITED STATES. 231 



these tracks were made by a quadruped ; because we find two 

 tracks near each other, succeeded by a long interval, and these in 

 two rows. The sketch is reduced four times, but is an exact copy 

 of the original. Those acquainted with the history of fossil foot- 

 marks will recognize the tracks of this species as identical with 

 those described by Dr. Cotta, in 1 839, in Saxony ; sketches of 

 which are given in the American Journal of Science, Vol. XXXVIII. 

 p. 255. The only difference is, that ours are more perfectly round- 

 ed. Dr. Cotta regards the extremity of the arch as the ends of 

 two toes, making the animal bidigitate. But our specimens make 

 it more probable that those extremities were the posterior part of 

 the foot, and that the toes were in front, and very short. He like- 

 wise could not find any succession of tracks ; but our specimens, 

 although not showing all we could wish, make it extremely prob- 

 able that the tracks had a quadrupedal origin ; and hence the spe- 

 cific name. 



Affinities of the Group. — I have already said enough, I trust, as 

 to the relations of the first genus ( Thenaropus) to batrachians, and 

 even to the Ranidse. The relations of the second genus {Anomce- 

 pus) may be a little more doubtful. The sprawling character of 

 its hind feet, so as to bring even the lower leg upon the ground, 

 corresponds better to some chelonians than to batrachians. Yet 

 the position of the feet, as shown on Plate 21, figs. 1 and 3, when 

 the animal was at rest, corresponds so nearly to that of the Ranidse, 

 that I think we may safely refer it to that tribe. Such a position 

 of the animal looks as if it moved by leaps, like the common frog. 

 But it is a large animal to advance in this manner ; I mean, large 

 among batrachians ; nor do the drawings, Plate 20, fig. 9, and 

 Plate 21, fig. 3, confirm this impression. If so large an animal 

 had advanced by leaps, is it possible that we should not meet with 



