160 PALAEONTOLOGY 



approximated to the most divergent of the three pairs ; that 

 of the first, a", being narrow in proportion to its Length, that 



of the second V, as broad as long, and the outermost, c , c", of 

 the third pair being oblong, but larger than that in the first 

 pair. In some places where the most approximated pair of 

 impressions, a, a", are deeply marked, they are complicated 1>\ 

 a fourth shallow and very small pit, a", 2 L, midway between 

 the third, a, and the outermost, a", of the pair of impressions. 



There are no clear or unequivocal marks of toes or nails on 

 any of the impressions which form the lateral pairs or triplets. 

 Their margins are not sharply defined, but are rounded off, and 

 sink gradually to the deepest part, which is a little behind the 

 middle of the depression. There is a slight variation in t lie 

 form and depth of the answerable impressions, but not such 

 as to prevent their correspondence being readily appreciable 

 through the whole of the extent here described ; that is to say, 

 the innermost of each of the three pairs here described as first. 

 A, second, B, and third, C, may be identified with the corres- 

 ponding innermost impression on the opposite side, and with 

 the same impression of the same pair in the three preceding 

 and the three succeeding pairs. 



The impressions selected for fig. 6-i clearly demonstrate 

 that the animal, progressing in an undulating course, made at 

 each action of its locomotive members, answering to the single 

 step of the biped and the double step of the quadruped, not 

 fewer than, in Protichnitcs 7-notatus, fourteen impressions, 

 seven on the right and seven on the left ; and in Protichnitcs 

 8-notatus, sixteen impressions, eight on the right and eight on 

 the left ; these seven and eight impressions respectively being- 

 arranged in three groups — viz., in Protichnitcs 7-notatus, three, 

 two, and two ; in Protichnitcs 8-notatus, three, two, and three 

 — the groups being re-impressed, in successive series, so 

 similarly and so regularly as to admit of no doubt that they 

 were made by repeated applications of the same impressing 



