﻿1851.] 



OWEN ON FOSSIL TORTOISE-TRACK. 



251 



is seen to sink down more steeply at its sides than towards the 

 bottom. 



The inference to be deduced from the above characters is, that 

 the impressions were made by a quadruped with the hind feet 

 larger and somewhat wider apart than the fore feet : with both hind 

 and fore feet either very short, or prevented by some other part of 

 the animal's structure from making long steps ; and with the limbs 

 of the right side wide apart from those of the left ; consequently 

 that the quadruped had a broad trunk in proportion to its length, 

 supported on limbs either short or capable only of short steps, and 

 with rounded and stumpy feet, not provided with long claws. There 

 are faint traces of a fine reticulate pattern of the cuticle of the sole at 

 the bottom of some of the foot-prints on the portion of sandstone ; and 

 the surface of the sand is generally smoother there than where not 

 impressed, which, with the rising of the sand at the border of the 

 prints, indicates the weight of the impressing body. The median 

 impression may be interpreted as due either to the abdomen or the 

 tail of the animal. If to the latter, the tail must have been very 

 thick, more depressed, or flattened horizontally, than rounded, and not 

 compressed or carinate below, as in the tails of the Crocodilia and 

 aquatic Batrachia. From the breadth of the impression a correspond- 

 ing great length of tail might be inferred from the analogy of the Rep- 

 tilia ; yet there is no indication of any bending or movement of such 

 a tail from side to side ; and an additional element for guiding our 

 choice from the two hypotheses of the cause of the median track is 

 afforded by the fact that, throughout the great length of the trail of 

 the quadruped, as exhibited by the plaster-casts, the median track 

 never curves in any degree nearer to the right or the left foot-prints, 

 but preserves an exact mid-distance between them. 



As the shape of the body and the nature of the limbs indicated by 

 the foot-prints accord best with those of the Chelonian reptiles of the 

 'estuary,' ' fresh- water/ or 'land' families, — the shape of the foot- 

 prints being decisive against the marine species, — the median groove 

 may have been scooped out of the soft sand by the hard and promi- 

 nent median surface of a plastron. If this were so, it may be in- 

 ferred that the species was a fresh-water or estuary tortoise rather 

 than a land-tortoise, the true Testudines carrying their trunk higher 

 when they walk than the more depressed Emydes do, and some 

 of them having the plastron concave on its under surface ; whereas 

 in the flatter Emydes, as e. g. Emys speciosa, the middle of 

 the fore-part of the plastron projects : and I am disposed to infer 

 a plastron to have made the impression rather than a tail, not only 

 from the shape of the impression, and its constant relative position 

 to the legs, but also from the fact of its being deepest where, 

 from the more confused or crowded grouping of the foot-prints, the 

 animal appears to have been moving more slowly or resting : where 

 the foot-prints are better defined, and indicate a steady rate of pro- 

 gress, the median impression is fainter, as if the trunk had been 

 better lifted from the ground ; and I may remark, that the difference 



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