CONNECTICUT RIVER SANDSTONE. 51 



under these circumstances, is invariably imperfect, whereas the impress of the 

 tarsus, represented by the Plate, is definite and, like that of the foot, unblemished. 

 Its terminal extremity is oval or rounded, and deeper and broader than the 

 proximal, and the tubercles of bones joining the lateral toes (figs, c c of PI. 

 31) are distinctly impressed. When the creature alighted upon the ground, it 

 impressed the form of the posterior foot and metatarsus, conjoined. 



But the most remarkable feature in this assemblage of impressions is the 

 impress of the os coccygis (PL 31, fig. D). It is heart-shaped, the apex pointing 

 forward, and its position, in regard to the tarso-pedal impressions, is central; and 

 its flattened or slightly concave impress indicates that the tail, or coccyx, of 

 the creature terminated abruptly, near to its junction with the pelvic bones. 

 That the author of these compound impressions moved by leaping, is not only 

 inferred from their formal arrangement, but is proved conclusively by certain 

 phenomena presented by the photograph (PI. 31). The momentum or propulsion of 

 the animal was such as to drive it far forward after its posterior feet had touched 

 the earth. The right foot grazed the ground to a considerable extent ere it 

 assumed a state of rest. The first contact of the toes with the ground occurs 

 at b b, which mark the furrow or trail produced by these slipping members, 

 and a a are similar grooves caused by the nails of the lateral toes. The original 

 specimen is fifteen times greater than the photograph, and the extent of earth 

 really brushed by the toes is more than twelve inches. Another fact concurs 

 to prove that the foot B slipped upon the stratum, in consequence of the momen- 

 tum by which the animal moved, as is seen in the accumulation of mud anteriorly 

 to the foot, which is gathered into massive ridges. These facts are conclusive, 

 that the foot touched the earth while the animal was moving with velocity 

 and force. 



It is difficult to find among existing reptiles the prototype of the creature 

 that impressed these singular footprints. Leaping animals are indeed found in 

 this class, but their feet present no analogies to those under consideration. Among 

 the lower grades of the mammalian class of animals, certain types occur, that 

 offer, in their pedal systems and mode of locomotion, a plausible basis of com- 

 parison, which is to be found in the marsupial tubes. The feet of the kangaroo 

 are conformable, as to the number and arrangement of the toes, and the meta- 

 tarsus, like that of the fossil impressions, is formed of a single bone, which rests 

 upon the earth with the foot, and leaves with it its conjoined . impress. The 



