148 AN ATTEMPT TO DESCRIBE THE ANIMALS THAT MADE 



rule which I have usually followed, where it could be adopted, has 

 been, to measure the lengths of the toes of the leptodactylous 

 tracks, from the point where the lateral front toes prolonged back- 

 ward cross each other. This at least does well for the relative, if 

 not for the absolute, length of the toes. 



These characters are more important and more easily ascertained 

 in those tracks which have only three toes directed forwards, 

 and these nearly straight, than in those with a greater number di- 

 rected forvi^ard, or which are much curved. In the first-named 

 tracks, I find the fourth or hind toe always the shortest ; the inner 

 toe, of the three directed forward, the next longest ; the outer one, 

 still longer ; and the middle one, the longest of all. This, I believe, 

 agrees with the relative length of the toes of birds. Where four 

 toes are directed forward, as Plate 15, figs. 6-9, Plate 16, figs. 4-6, 

 and also Plate 11, figs. 1 and 2, the same order is observed. It is 

 generally the same in the five-toed species, as Plate 13, fig. 2, 

 and Plate 14, fig. 1. But sometimes, as in Plate 16, fig. 2, the out- 

 er toe but one is longest, and the outer one much the shortest, as in 

 many of the living Ranidae. 



5. Divarication of the lateral toes. — In many living species, as, 

 for example, the Palmipedes among birds, this is a very constant 

 and reliable characteristic. Nor is this constancy confined to the 

 web-footed animals. Where the toes are free, they diverge at a 

 pretty constant angle ; and so it seems to be with the fossil foot- 

 marks. I speak now of those where three toes are directed for- 

 ward ; for the chief application and use of this character are con- 

 fined to these. They do, indeed, diverge a few degrees more or 

 less in different specimens ; but the variation is so limited, that a 

 practised eye often recognizes a species by this mark. The an- 

 gle is measured by lines drawn from the tips of the lateral toes to 

 the middle of their posterior extremity. 



