26o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



3. The varying position of the median ridge with reference to the lateral 

 ridges points to the conclusion that the transverse body was at the time char- 

 acterized by a mesial sinus or upfold, and that the axis of this fold played to 

 the right and left as a fold might in the flexible muscular foot of a crawling 

 mollusk .... 



4. The pressed sand on the slopes and over the crest of the transverse ridges 

 eliminates from the processes by which the ridges may have been made the 

 backward push of the posterior margin of such an animal as the trilobite or 

 of any transverse gill plate so placed as not to permit, under the condition 

 in which the creature moved, the smoothing down of the successive ridges by 

 some soft, pliable body still further an derriere. 



.... The trail itself, therefore, it seems safe to state, was made by some 

 flexible body like the mesially up-curved 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 vvhich made the trail 

 reached the end of the track and there, resting on the sandy bottom, left an 

 impression 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 Climactichnites. 



The larger of the terminal impressions measured at Bidwell's crossing gave 

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



The manner in which several of the trails approach in a common direction 

 and end close to each other in sedentary impressions is exactly what takes 

 place in the case of the trails of many gregarious aqueous forms, which 

 crawl up a beach or a partly exposed sand bar and rest on the dry sand. 



Among some fine specimens of Climactichnites youngi Chamberlin, 

 received from Rev. A. A. Young of New Lisbon, Wisconsin, in 1886, 

 there was one good example (pi. 38) of the outline of a terminal 

 elongate oval body of essentially similar outline to those subsequently 

 found by Woodworth at the ends of the trails at Mooers, New York. 

 I put the specimen aside in the hope that more and better ones would 

 be found so that we would have evidence upon which to base conclu- 

 sions as to the animal that made the trail. 



Woodworth suggests that the animal crawled up from the water at 

 low tide across the ripple-marked and smooth beach sand ; that it was 



