84 ROYAL SOCIETY OF CANADA 



prints is variable, but H. Ilardingi better represents the type of the 

 genus than H. Logani. 



Sir William's description of H. Ilardingi is as follows (" Air- 

 breatherg/' p. 8) : "Dr. Harding found on one of these slabs a very 

 distinct series of footprints, each with four toes and a trace of the fifth." 



As the stride in H. Hardingi was five and a half inches, the track 

 was probably that of an animal more than twice this length, i. e., more 

 than a foot long. The width of the track was two and a half inches. 



In this species the |)rint of the inner pair of toes was faint, indeed 

 as regards the fore foot there was not any print of the first digit. There 

 were, especially as regards the fore foot, three master toes, which always 

 made a strong impression; in the hind foot this preponderance of the 

 three central digits is not so marked, but still it is observable. The ab- 

 sorption, or weakening of the side toes, was thus in progress in these 

 early forms. This process, if continued mainly in the fore foot, would 

 in time give a species which would have the characters of Asperipes, in 

 which the fore foot shows only three toe marks, but the hind retains five, 

 and a form of footprint, not unlike that of the hind foot of Hylopus 

 Hardingi. 



The tendency to this absence of the print of the outer toes is seen 

 in the more advanced footmarks in the typical series of footprints of 

 H. Hardingi, where only three toe marks can be observed in the print 

 of the fore foot. 



In examining the track of this animal in detail, it will be seen that 

 the creature had the habit of placing the hind foot directly behind the 

 fore foot in walking, so that the two prints made by these feet were just 

 clear of each other. An exception is seen in the first track of the series 

 where the print of the hind foot overlaps that of the fore foot; and a 

 partial exception is seen in the second pair of footprints where the third 

 digit is flexed, apparently by coming in contact with the fore foot before 

 that had been removed to make another step. In the succeeding foot- 

 steps of the series it will be observed that the toes are not bent, for in 

 these cases the two feet did not interfere. 



The reduction in the number of the toe marks of the hind foot in 

 such ungulate forms of moderate size as Hylopus cannot be traced to 

 forms with fewer toes, for though there are several genera that possess 

 five toes on the hind foot, I know of none with four, except the blunt- 

 toed genus Nanopus and the genus Dromillopus described on a later 

 page. But in species oî a smaller size, Ornithoides presents us with a 

 form in which the three master toes of each foot, only, are represented 

 in the footmark. Further than this the reduction in the number of 

 digits seems not to have gone; at least the author is unacquainted with 

 any Carboniferous species having a smaller number of toe prints. 



