218 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 24, 



scribed, we have the group of three impressions, a, «', a", the trans- 

 verse pair, b, V, and the widest pair, c, c', in which the outer and 

 larger impression is divided into two, c', c". 



Neither in this nor in the preceding series does any impression ap- 

 pear to be modified or in any degree obUterated by the print of another 

 foot coming into the same place. 



The median interval between the right and left of the first pit in 

 the group of 3 impressions, a!, is 3 inches 9 lines ; between the two 

 pits in the same sets forming the apex of the triangle, a!\ 4 inches 

 8 lines, and between the third, «, 3 inches 2 lines. These measure- 

 ments are taken from the inner border of the right and left impres- 

 sions respectively. The interval between the innermost, b, of the 

 transverse pair of impressions is 3 inches 2 lines, and between the 

 outermost, 6', from their outer borders 5 inches 8 lines : the interval 

 between the longitudinal pairs, c', c", from their outer border is 5 

 inches 3 lines. The length of each series of three sets of impressions 

 is from 5 inches to 5 inches 3 lines, and this distance is very regularly 

 preserved throughout the series of tracks. Thus each series presents 

 eight distinct impressions on each side, IX, 1 ^, and tallying impres- 

 sions of each of the eight can be determined in each successive series, 

 2i, 2R. 



From this it is to be inferred that they were made by the same 

 parts respectively ; that is, that the impressions were repeated by the 

 same limbs or impressing instruments at each successive series. Con- 

 sequently if we regard each series as indicating the nature of the 

 individual that impressed them, we must conclude it to have pos- 

 sessed either eight pairs of impressing instruments, or three pairs of 

 limbs so divided as to leave 3 prints, 2 prints, and 3 prints in longi- 

 tudinal succession on both the right and the left sides, and suffi- 

 ciently long and flexible to make a step co- extensive with the space 

 occupied by the entire series of such limbs ; these impressions seve- 

 rally presenting characters so distinct in the same series of A, B, C, 

 as to forbid the conclusion that they were made by the same instru- 

 ments differently applied at regularly alternating intervals or distances 

 in such series. 



We have clearly, therefore, indications of the same kind or genus 

 of animal in the present, as in the preceding series of tracks, but the 

 difference in the proportions and arrangements of the individual im- 

 pressions in the determinable groups indicates a difference of species. 

 There are two other series of tracks of the Protichnites 8-notatus 

 repeating very recognizably the characters above described. 



3. Protichnites latus. PI. XI. 



A slab of the sandstone 8 feet long* by 2 feet wide shows three 

 series of the impressions, two extending lengthwise and crossing each 

 other very obliquely, and the third crossing both the others trans- 

 versely. In the track which traverses the whole length of this slab 

 the impressions of the feet are deeper and larger, whilst the median 



* This track has a still greater extension on the plaster-casts taken from the 

 sandstone-surface of which the slab here referred to is a portion. See the Plan, 

 PI. VIII. B. 12. 



