1)04 NEW YORK STATE MUSEUM 



posterior margin of the expanded, retractile foot of a large 

 crawling organism. 



It remains to note the nature of the terminal impressions 

 associated with many of the trails in the Mooers occurrence. In 

 the first place, the postulate above made that the trails were 

 made progressively toward these oval terminal impressions may 

 now be explained by stating that, where the relation of the oval 

 impressions to the trail can be made out, it is clear that the 

 oval impression has obliterated a portion of the trail which once 

 extended into the area of the oval impression; this is taken to 

 mean that the animal which made the trail reached the end of 

 the track and there, resting on the sandy bottom, left an impres- 

 sion of the outline of some marginally relatively rigid structure 

 of the ventral surface. Had the organism started out from this 

 oval area, it is obvious that the oval would have been partly 

 effaced and merged into the trail. The complete adjustment of 

 the oval terminal impressions to the trails thus becomes of 

 extreme interest; for it must be that in these impressions there 

 is a clue to the outline of the organism which produced Olimac- 

 tichnites. • 



The larger of the terminal impressions measured at Bidwell's 

 crossing gave a length of 16 inches and a breadth of 6 inches. 



The oval impressions are somewhat more depressed in the 

 sand than the trails, particularly toward the posterior margin 

 of the impressions [see plate A to the right of the knife]. In 

 figure 1, a sketch is made of what was interpreted to be the 

 general outline of the marginal groove of the oval impressions; 

 but, either because the impressing body was tilted posteriorly 

 downward so that it did not make so broad an impression 

 anteriorly or because it was wider posteriorly than anteriorly, 

 most of the distinct impressions are rather more pointed 

 anteriorly than is shown to be the case in the diagram. There 

 is also a broad swell in the center of the impressions. In the 

 study of the forms which was made in the field, no traces of 

 appendages or other ventral structures were made out. We are 

 thus left to the trails, to the outline of the creature, and to the 

 broadly undulating impression of the vprtf ra i sur face to infer 

 its nature. 



