1852.] OWEN — POTSDAM SANDSTONE FOOT-TRACKS. 217 



than 6 feet. The most constant of the small impressions are those 

 which are nearest the median track, c, and which have been described 

 as the innermost of the third pair, but which first arrest the eye as 

 superadded foot-marks, occurring pretty regularly at intervals of from 

 4 inches to 4^ inches along the whole track. 



There are three other series of tracks referable to the Frotichnites 

 7'notatus. 



2. Protichnites octo-notatus. PI. X. 



The series of foot-prints, here described as the Protichnites 8-no- 

 tatus, extends for 5 feet 5 inches along a surface of hard sandstone, 

 which has been rubbed by the ice. This track is represented by 

 plaster-casts. It is seen on the Plan, PL VIII. B. 6. In this series 

 the impressions of the feet are deeper and the median track is much 

 fainter, yet it continues to show the alternately deep and shallow 

 character, its traces being visible at regular intervals, which are, 

 however, longer than those that divide the deeper parts of the same 

 groove in the first-described series of impressions. 



In the present series the small innermost impressions, c, are re- 

 peated at intervals of 5 inches ; the distance between the right and 

 the left of these impressions is 2 inches, being less than half their 

 longitudinal interval ; whereas in the former slab the transverse in- 

 terval is exactly half the longitudinal one. 



The larger and more exterior depressions present also a somewhat 

 different arrangement from those first described. Where they are 

 most clearly and regularly impressed it is as follows : — on the outside 

 of the small innermost impression, c, there is a pair of larger im- 

 pressions, c', c", closely approximated one behind the other, in the 

 direction of the track, the longitudinal extent of this pair of impres- , 

 sions being 1 inch. The next pair of impressions, b, b', answering to 

 the middle pair before described, and here noticed in the contrary or 

 retrograde course, are placed nearly transversely and are wider apart 

 than the longitudinal pair, the innermost being the largest, and the 

 diameter of the pair 1 inch 8 lines. Then follow three impressions, 

 a, a\ «", forming an inequilateral triangle, with a broad base turned 

 inwards and the apex outwards, the impression forming which («") is 

 the largest of the three, although they are of nearly equal size, having 

 a diameter each of about half an inch. These three impressions an- 

 swer to the three, a, a!, «", PI. IX., which have been described as 

 forming the first pair of impressions with the accessory impression 

 in the Protichnites 7-notatus ; but the three are here so distinct and 

 remote that the pair could only be chosen arbitrarily. The middle 

 or second pair, 6, b\ answers to the same in the impressions first 

 described, with the difference of direction above noted : the third pair 

 differs in the more constant and complete division of the larger outer- 

 most impression into two pits, c, c'. In none of these impressions are 

 there distinct and unequivocal traces of claws or digital divisions ; 

 they seem rather to have been impressed by one limb, or division of a 

 limb, terminating in a hard, obtuse, subangular point. 



The arrangement of the impressions just described is repeated with 

 little modification throughout this series of tracks ; that is to say, 

 taking them in the order in which those of the first series were de- 



