34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



the same diagonal angle as shown in figure 14. The impressions 

 forming the two rows on either side of the tail drag are regularly 

 alternating. The outer or third row is composed of the largest and 

 most distinct markings, but their spacing is the same as those of the 

 other two rows. The impressions found on either side of the tail 

 drag are quite certainly made by the feet, but as to the origin of the 

 third row, one cannot be certain whether it was made by a foot or by 

 some other appendage. However, the regularity of spacing and close 

 conformity to the other rows leaves no other conclusion than that all 

 were made by the same animal. Whether the normal trail would 

 consist of four rows of tracks, as in Bifurculapes,^ which in some 

 specimens shows only three, there is no way of determining at this 

 time. Only by the discovery of additional specimens can we hope to 

 clear up this point. While I have been unable to definitely classify 

 these tracks they give every indication of having been made by some 

 invertebrate animal and for the present at least they will be so 

 regarded. 



The specific name is in honor of Prof. H. H. Nininger of McPher- 

 son, Kansas, who found the type specimen and generously donated 

 it to the national collections. 



PALEOHELCURA TRIDACTYLA Gilmore 



Paleohelcura tridactyla Gilmore, Charles W., Smithsonian Misc. Coll., 

 Vol. 7y, No. 9, 1926, pp. 31-34, pi. 12, fig. I, text fig. 20. 



The discovery of a second specimen (No. 11,499, U. S. N. M.) 

 of Paleohelcura tridactyla is of interest because the tracks were found 

 in situ in the Coconino sandstone, at about 150 feet above the base 

 of the formation and not far distant from where the type was dis- 

 covered. The type was a loose slab found lying on the hillside below 

 the Hermit Trail about 125 feet above the base. 



The second specimen adds nothing new to our knowledge of the 

 species, as it exhibits the same tridactyle impressions with a tail drag 

 in the center of the trackway. 



Genus UNISULCUS Hitchcock 



Unisulcus Hitchcock, Edward, Ichnology of New England, 1858, p. 160. 



The genus Unisulcus was established by Hitchcock for a group 

 of simple trails which he regarded as having been made by naked 



^ Hitchcock, Edward, Ichnology of New England, 1858, pp. 153, 154, pi. 30 



