REPORT OF THE STATE PALEONTOLOGIST 1902 



903 



in the manner indicated in figure 3, in imitation of the alternate 

 contractile and extensile movements of a crawling organism, 

 whose posterior margin the plate represented, it was possible 

 to produce transverse ridges 

 with the medial swell and the 

 forward curved lateral ridges 

 apparently overlain in succes- 

 sion by each new ridge. The 

 whole surface of each ridge, ex- 

 cept on the outer parts of the 

 lateral ridges; was pressed down 

 on both slopes, the posterior 

 slope being steeper than the an- 

 terior slope in this process, just 

 as is the case with Climactich- 

 nites. This difference of slope 

 must necessarily arise where a 

 transverse body is drawn for- 

 ward, pushing up a ridge over 

 which it is drawn in the making 

 of the next ridge at its proper 

 interval. 



The experiment with the artificial plate showed that, with 

 such a rigid body, rigid ridges only could be produced; further- 

 more the ridges are at right angles to the margins, the central 

 swell is equidistant from those margins, and, while the forward 

 bend of the transverse ridge in passing over the central swell 

 is slightly shown, the ridges themselves have not that oblique 

 position w T hich is frequently the characteristic feature of seg- 

 ments of Climactichnites. The comparison of the trails natural 

 and artificial has therefore led me to the conclusion that Climac- 

 tichnites could not hafve been made by the rigid carapace of a 

 trilobite; moreover, there is no trilobite known in the Cambrian 

 with an outline of the pygidium which could have produced the 

 result, nor have recent discoveries concerning the natatory 

 organs of the trilobites shown in the group the existence of 

 natatory or gill plates such as are found in the more modern 

 Xiphosura. The trail itself, therefore, it seems safe to state, 

 was made by some flexible body like the mesially up curved 



Fig. 3 Showing successive positions of 

 scraper in experiment to. imitate Climac- 

 tichnite trails. (1) Position of scraper at 

 end of long forward sLpe of a trans- 

 verse ridge.; (2) position of scraper after 

 it has been raised up, overridden a trans- 

 verse ridge, and begun to make a second 

 frontal slope; (3) position as at 1, but 

 showing cross section of completed trans- 

 verse ridge in the rear. Movement in 

 direction of the arrow. 



