1852.] OWEN — POTSDAM SANDSTONE FOOT-TRACKS. 223 



The recognition of the real nature of this superadded print also 

 leads to the recognition of the succession of the prints in progressive 

 series of three groups, two of which seem to consist of a pair of prints, 

 as in the Protichnites l-notatus"^. That peculiarity could not, I be- 

 lieve, have been recognized, or satisfactorily confided in, without the 

 aid and hght of the analogies furnished by the more numerous and 

 extensive, clearer and better-marked, impressions which have now 

 been submitted to us by their zealous and indefatigable discoverer and 

 collector. I need scarcely say, therefore, that although the foot-prints 

 of a Tortoise are those to which the original series of the Potsdam 

 sandstone impressions bore the closest resemblance, I have now the 

 conviction that they were not made by a Chelonian reptile, nor by 

 any vertebrated animal. 



The impressions selected for Plates IX. and X. 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 Protichnites 7-notatus, fourteen impressions, seven on the right 

 and seven on the left ; and in Protichnites S-notatus sixteen im- 

 pressions, eight on the right and eight on the left ; these seven 

 and eight impressions respectively being arranged in three groups ; 

 viz. in Protichnites 7-notatus, 3, 2, and 2 ; in Protichnites ^-notatus, 

 3, 2, and 3 ; the groups being reimpressed, 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 instruments, 

 capable of being moved so far in advance, as to clear the previous 

 impressions and make a series of new ones at the same distance from 

 them, as the sets of impressions in the series are from each other. 

 What then was the nature of these instruments ? To this three replies 

 may be given, or hypotheses suggested : — they were made, either, 

 1st, as in the case of quadrupedal impressions, each by its own limb, 

 which would give seven and eight pairs of limbs to the two species 

 respectively ; or, 2ndly, certain pairs of the limbs were bifurcate, as 

 in some insects and crustaceans, another pair or other pairs being 

 trifurcate at their extremities ; and each group of impressions was 

 made by a single so-subdivided limb, in which case we have evidence 

 of a remarkably broad and short hexapod creature ; or, 3rdly, three 

 pairs of limbs were bifurcate, and the supplementary pits were made 

 by small superadded limbs, as in some crustaceans ; or, 4thly, a single 

 broad fin-like member, divided at its impressing border into seven or 

 into eight obtuse points, so arranged as to leave the definite pattern 

 described, must have made the series of three groups, by successive 

 applications to the sand. 



The latter hypothesis appears to me to be the least probable ; first, 

 as being most remote from any known analogy, and secondly, because 

 there are occasional varieties in the groups of foot-prints which would 

 hardly accord with impressions left by one definitely subdivided in- 

 strument or member. Thus in the group of impressions marked 1 i, 



* This will be seen, on a comparison of the original and entire series of foot- 

 prints, more satisfactorily than in the small portion figured in Plate XIV. A. 



ci2 



