202 AN ATTEMPT TO DESCRIBE THE ANIMALS THAT MADE 



outer and middle toes, 1.6 inch; between the middle and hind toes, 

 3.3 inches. Toes slightly curved. 



It is clear, I think, from the angles of divarication of the for- 

 ward toes, as well as from the length of the toes and the posi- 

 tion of the lateral or hind toes, that the front track of this 

 specimen must have been made by a left foot, and the other by a 

 right foot ; although I feel a little doubt whether the toe d is the 

 hind toe of the fore foot, as it only shows its extremity. The hind 

 foot, as appears from the above measurements, is smaller than the 

 fore foot ; which is not usual in batrachians or lacertilians. Upon 

 the whole, I cannot make out this track to be of quadrupedal origin, 

 and yet its general character is such as to leave me still in doubt 

 whether the animal was not a quadruped. 



One other specimen of the tracks of this species (No. 163 of 

 Cabinet), split twice asunder, shows the forms delineated on Plate 

 15, figs. 17-19. Here it is not obvious that two tracks are united. 

 Indeed, had not the case above given furnished the clew, we should 

 not suspect from this specimen that more than one track existed. 

 The occurrence of two specimens of these double tracks strength- 

 ens the suspicion, that the animal that made them (Pledropus lon- 

 gipes) was a quadruped. 



Genus IX. TRIiENOPUS. 



Feet tridactyle in front, plantigrade ; divarication small : toes 

 very slender ; hind toe proceeding from the extremity, or near the 

 extremity, of the heel. Heel very slender. Gregarious. 



Remark. — The distinction between this and the preceding ge- 

 nus is not striking, and perhaps not permanent. It consists in the 

 much more slender and delicate character of the whole foot, and in 

 the position of the fourth toe. But I have some reason to suspect 



