THE FOSSIL FOOTMARKS OF THE UNITED STATES. 245 



Struck with the resemblance to the trail of a tortoise upon mud. 

 Yet after the animal passed, a thin layer of mud was deposited, 

 after which other animals walked over it and a shower of rain fell 

 upon it, so that the tracks of the Helcura are indistinct. The toes 

 cannot be distinguished ; nor can the successive tracks of the same 

 foot be seen very certainly. 1 cannot, however, doubt that these 

 trails were made by a chelonian, and by a different species from 

 any other whose tracks I have met upon this sandstone. They 

 have been found only at Turner's Falls. A second fine example 

 may be seen in Mr. Marsh's collection, a sketch of which is 

 given on Plate 23, fig. 3. Plate 21, fig. 1, shows also the trail of 

 Helcura. 



Affinities of the Group. — It seems unnecessary to add much to 

 the preceding descriptions, to make it probable that the genera An- 

 cyropus and Helcura were chelonians. No other animals that I 

 know of would leave such footmarks and trails. The approxima- 

 tion of the tracks, as shown on Plate 19, fig. 4, shows that the 

 Ancyropians moved forward very slowly, just as tortoises now do. 

 Their tail and feet, also, were frequently trailed over the mud, as 

 was done by the Helcurans. And if I have not mistaken the 

 characters of these genera, the conclusion seems forced upon us 

 that they were chelonians. 



Group IX. ANNELIDS or MOLLUSCS. 



Track a curved or looped furrow, of various sizes. 



Genus XXII. HERPYSTEZOUM. 



Characters the same as those of the group. 



