THE FOSSIL FOOTMARKS OF THE UNITED STATES. 155 



general level of the stone, while behind this ridge is a depression, in 

 the bottom of which are minute ridges, radiating backward a consid- 

 erable distance, which I have represented on Plate 5 bj lines, the 

 whole heel having the appearance of a brush. I formerly suggest- 

 ed, that this might have been produced by coarse hairs upon the 

 animal's heel ; but I now give up that idea, and imagine it to have 

 been produced by radiating rugosities on the heel, or by the partial 

 adhesion of the mud to the heel, as the animal raised its foot, con- 

 joined with the subsequent action of the water ; and I have some- 

 times thought it possible that the whole might be merely slight rip- 

 ple-marks. But whatever may have been the origin of these marks, 

 we may be sure that a large and rather remarkable heel belonged 

 to the animal. 



The long and narrow heel is a common one in these footmarks. 

 In many instances, it seems to have been made by a long metatarsal 

 or metacarpal bone, which did not lie horizontally upon the ground, 

 but was inclined at various angles, according to the manner in 

 which the animal pressed upon it, and moved forward. Hence the 

 imprint would vary in different specimens, and its posterior termi- 

 nation be difficult to fix exactly. This character is shown on figs. 

 2 and 3, Plate 9, of Pleciropus minitans, where it is obvious that 

 the heel lay in a sloping position. In the Anomcepus scambus the 

 whole of the tarsal or carpal joint is sometimes exhibited, and a part 

 of the fore leg, as in Plate 13, fig. 4. At other times we see a 

 graceful swelling out of the heel a little in advance of the tarsal or 

 carpal joint, as in figs. 3 and 1 of Anomcepus scambus. The same 

 is sometimes seen on Pleciropus minitans, Plate 10, fig. 1. 



The long heel of the hind foot of Macropierna, as already ob- 

 served, may have been a toe ; indeed, it bears a strong resem- 

 blance to the posterior toe on the hind foot of the Phyllurus Milii 



