2y'^ SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



If we picture in our imagination a trilobite with a series of twelve 

 pairs of leg's posterior to the cephalon (figs, i and 2), and five pairs 

 of cephalic legs, walking on the smooth or rippled surface of fine 

 wet sand exposed at low tide, I think we can readily explain the 

 Protichnitcs tracks on the Potsdam sandstone. Such a series of feet 

 would make varied and complex series of tracks that would dififer in 

 depth,' definition, and details of grouping with the var3'ing degree of 

 consistency and hardness of the surface over which the animal was 

 traveling and its method of moving. I have fine trilobite trails made 

 on the surface of sandy mud that show the imprint of a considerable 

 portion of the legs. On a hard surface the animal touched only the 

 extremities of the legs, but on a muddy surface the terminal joint 

 would sink in and other joints would leave an impression. 



The particular trilobites that left the tracks on the beaches of Pots- 

 dam sandstone time were undoubtedly species of the genus Dicello- 

 cephalus. Individuals of this genus attained a large size, and Dicel- 

 loccphalus hartti occurs in the Potsdam sandstone both north and 

 south of the Adirondack ]\Iountain area of New York. 



With our present information of the structure of the trilobites I 

 do not think that we can consider Climactichnites as the trail of a 

 trilobite. This has been referred to under discussion of that genus 

 (pp. 259-261). 



Summary. — The Protichnitcs tracks found on the surface of layers 

 of Potsdam sandstone were made by trilobites of the genus Diccllo- 

 ccphalus. 



The trifid imprint resulted from the impress of the end of the 

 terminal joint of the trilobite's leg with its three movable spines. 



The trails named Climactichnites were not formed by trilobites 

 and have a quite different origin from the Protichnitcs tracks. 



PROTICHNITES SEPTEMNOTATUS Owen 



Plates 46 and 47 



Protichnites septctn-notatus Owen, 1852, Quart. Journ. Geol. Soc. London, 

 Vol. 8, pp. 214-217, pi. 9. (Description of species.) 



I shall not attempt to insert the synonymy of this species. The 

 principal papers treating of the genus have been mentioned. In a 

 future paper on the trilobite I may consider in detail the various 

 series of tracks to which Owen gave specific names. At present I am 

 inclined to consider that all the Beauharnois tracks were made by one 

 species of Dicelloccphalus and the Keeseville, Essex County, New 

 York, tracks by another species. The latter tracks are on a finer- 



