228 AN ATTEMPT TO DESCRIBE THE ANIMALS THAT MADE 



had been worn off, and I then supposed that a three-toed animal 

 must be a biped. I suggested, however, their resemblance in other 

 respects to those of a marsupial quadruped, but left the case unex- 

 plained. This was in 1840. At the meeting of the Geological 

 Association in Boston, in 1842, I described the same track, from a 

 specimen discovered by Dr. Deane, and presented to me, under the 

 name of Saxiroidichnites Deiveyi. This description, with a draw- 

 ing, was published in the Transactions of the Association, and I 

 there stated that " this is the first example in which any of the 

 numerous tracks upon the sandstone of the Connecticut valley 

 were made by a quadruped." Dr. Deane, in 1845, published a 

 drawing and description of the same specimen, as containing the 

 tracks of a quadruped. But the discovery of still better specimens, 

 from one of which (No. 136 of my cabinet) Plate 22, fig. 1, was 

 copied exactly, gives us a clearer insight into the character of the 

 animal, especially as to its mode of progression. We can see on 

 that drawing, that the feet on the right side of the animal uni- 

 formly pointed a little to the right, and those on the left to the left ; 

 and that it must have advanced by regular steps, like a common 

 mammiferous quadruped. The slab on which this row of tracks 

 occurs is represented on Plate 20, fig. 10. On it are four rows 

 of jEthyoptis minor, and two tracks of Helcura littoralis. Plate 

 23, fig. 3, shows another slab in Mr. Marsh's cabinet, with tracks 

 of Anisopus. 



Species 2. Anisopus gracilis. (PI. XVI. Figs. 3, 4.) 



Nos. 141, 158, in Cabinet. Numerous specimens in Mr. 

 Marsh's cabinet. 



Hind foot. — Divarication of the lateral toes, 40° ; of the inner 

 and second, 15° ; of the second and third, 10° ; of the third and 



