478 RICHARD SWANN LULL OX 



(lelined. Pliuitigrade is that foot posture in which the whole sole and heel are applied 

 to the ground in normal progression as in Otozouni. Tiie term calcigrade is used by 

 Hitchcock to define a track in which the heel impression is deeper than the anterior part 

 of the foot. The present author would confine its use to a posture as of the sitting 

 Anornoepus which in its progression is digitigrade (see figs. 19 and 20) . In a digitigrade 

 foot only the digits and the distal ends of the metatarsals are applied to the ground as in 

 Gigandipus. Anchisauripus has the posterior part of the foot skeleton raised so high as 

 almost to warrant the application of the term semidigitigrade being applied to it. Such 

 a foot posture may lead to a complication of the pads seemingly without reference to the 

 overlying bones. 



Summary of taxonomic characters. — (a) Ordinal. Whether habitually bipedal, 

 occasionally quadrupedal, or habitually quadrupedal. Character of claws, especially of 

 manus. General form of manus and pes. 



(b) Generic. Relative length of foot to limb. Width of trackway. Presence or 

 absence of caudal trace. Relative size and contrasted characters of manus and pes. 

 Number of digits of manus and pes. Position of hallux. Presence and character of meta- 

 tarsal or heel impression. Varying degrees of plantigrady or digitigrady. Complexity of 

 pads. 



(c) Specific. Length of digits,' actual and relative. Size of animal. Angle of 

 divarication of digits. Peculiarities of form. 



Classification. 



The classification of the forms which made the footprints is a matter of extreme diffi- 

 culty as the true nature of many of the footprint genera cannot be ascertained in the 

 present state of our knowledge. The best that can be done in the matter is to place the 

 more obvious forms in what seems to be their proper relationship, reserving, for the pres- 

 ent, an expression of opinion upon the remainder of the genera. Amphibia must have 

 inhabited the Triassic estuaries Init with the possible exception of Shepardia, their tracks 

 cannot be identified as of such, all of the better known forms evidently belonu-ino' to the 

 Reptilia. 



A scheme of classification based upon that proposed by Osborn (:03a) may be given 

 as follows : — 



