ICHNOLOGY. 



183 



V, and 2 in the third, c, c\ which is followed by a repetition of 

 the group of 3 prints, a, a', o!\ making the numbers in the 

 three successive groups, 3, 2, 2 ; the three groups of impres- 

 sions being recognizably repeated in succession along the whole 

 series of tracks on both sides of the median groove. 



■L_i 



Fig. 82. 

 Protichnites 1-notatus (Cambrian). 



The principal footprints are disposed in pairs, placed with 

 different degrees of obliquity, in each of the three groups 

 towards the median track ; the innermost print in the second, 

 B, and third, C, pairs, which are best marked, being usually 

 rather more than half the size of the outer print, V and c'. 



The two footprints of the same pair are a little further 

 apart from each other, in the three succeeding pairs, as at a\ 

 a", b, l>, c, c, especially in the second and third groups of each 



