FOSSIL FOOTPRINTS OF THE JURA-TRIAS. 477 



from the axis of the foot while the chiw of digit III is invariably bent inward toward the 

 middle of the ti-ackway. These criteria refer to isolated tracks ; where there are two or 

 more footprints in a row there is generally no difficulty in distinguishing the right from 

 the left foot. 



5. The number of digits is a valuable character for use in systematic work, though 

 frequently the entire number does not impress, or the mark of the hallux is such as to be 

 easily overlooked. The handprints of Anomoepus or of Chirotherium are very likely to 

 be defecti^'e because each animal pressed so lightly with the manus. 



6. The length oi the toes. Itoth actual and relative, the amount of protrusion or 

 exsertiou of the middle toe beyond the lateral ones and the distance between the tips of 

 the latter are valuable criteria. 



7. The angle of divarication of the toes is a somewhat variable character, that 

 between the lateral ones (digits 11 and IV) being the most constant. This is measured 

 by drawing lines througli the axes of the digits and reading the angles of intersection 

 with a protractor. As these points of intersection rarely coincide, the angle between the 

 lateral toes is generally greater than the sum of the individual angles. It has been quite 

 difticult to make the descriptions given in the present work agree absolutely with those of 

 Hitchcock in this regard even where the same specimens have Ijeen measured. 



8. The character of the claws, or their aijsence, is a criterion of great importance. 

 In the dinosaurs the feeding habits have been deduced from the claw structure and hence 

 the separation of the genera into their proper orders is largely based thereon. Thus it is 

 impossible to imagine Anomoepus, with the small rounded claws on manus and pes, as 

 having carnivorous habits, while the pointed claws and powerful hallux of Anchisauripus 

 would place it among the Theropoda even if we did not associate the genus with the car- 

 nivorous Anchisaurus. In some cases it is quite difficult to judge, especially of the claws 

 of the anterior digits of the pes, which, as mentioned above, only become curved trench- 

 ant weapons in proportion as those of the manus are reduced or lose their efficiency as 

 prehensile organs. One should remember that among herlnvorous ungulate mammals the 

 Ancylopoda,^ and Agi-iochoerus - are bluntly clawed forms, while Mesonyx, a creodout. 

 was hoofed. 



9. The presence and character of the metatarsal or " heel " impression found in the 

 Anoiitoepodidae is a very distinctive character and the relative lengths of heel and foot 

 o-ive about the only definable specihc distinction between Anomoepus scambus and A. 

 intermedius. 



1(1. Varying degrees of plantigrady and digitigrady nuiy be noted and may thus be 



I Beddard, Cambridge natural liLstury, iy02, vol. 10, p. 211. 

 - Wortiuan, Bull. Aiiier. mus. nat. hist., 1895, vol. 7, p. 145. 



