12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



side consists of a uniform series of elongated depressions that stand 

 diagonally to the line of direction. These are quite regularly spaced, 

 averaging about 15 mm. apart. The outer ends of the diagonal tracks 

 are somewhat enlarged backward, whereas the inner end gives ofif 

 a sharp spur that is directed forward and inward. Over all, these 

 diagonal impressions have an average length of about 27 mm. A 

 second, and supposedly median row of elongated impressions, but 

 less clearly registered, parallels those just described. They also have 

 a diagonal trend, paralleling in direction but usually alternating with 

 those of the outer row. 



This trail seems to be undescribed and when more perfect examples 

 are found, there will be little difficulty in fully characterizing it. The 

 character of the trackway points clearly to its invertebrate origin, 

 though at this time I have no suggestion to offer as to the particular 

 group of animal life to which it may be attributed. 



A second trail. No. 11,693, U. S. N. M. (see pi. 4, fig. 2), collected 

 by Mr. G. E. Sturdevant in 1927, from the uppermost track-bearing 

 horizon of the Supai formation, on the west side of O'Neill Butte, 

 represents another undescribed trackway of peculiar kind, the details 

 of which, as in the preceding, are not altogether clear. This trackway 

 has a total length of 330 mm. ; width about 65 mm. : length of stride 

 about 25 mm. It consists of two parallel rows of curved, pointed, 

 finger-like markings, between which are irregularly shaped, subround 

 impressions of spasmodic occurrence. The tracks of opposite sides 

 seem to alternate, although in some few instances they are opposite. 

 The finger-like impressions stand diagonally to the line of movement 

 and seem to 1)e directed forward, though from this specimen alone 

 one cannot be sure of the direction of movement. The irregularity 

 of the impressions (see fig. 6). especially of the two rows, does not 

 permit of a satisfactory diagnosis, and for that reason I refrain 

 from naming it, though it undoubtedly represents a form new to this 

 ichnite fauna. 



In plate 3. figure 2, is illustrated a kind of track that has been 

 observed on numerous occasions in the Supai formation, but which 

 has not yet been found in the form of a definite trackway. While 

 this type of track may be easily recognized, none of the examples 

 found gives any idea of a continuous trail, the individual tracks being 

 placed here and there and apparently without rhyme or reason. Occa- 

 sionally two and three will be found, one placed behind the other. 



