8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



doubt as to their being cospecific. The differences noted in a compari- 

 son of these two specimens illustrates the need of an abundance of 

 material in the study of fossil tracks if an investigator is not to be 

 led astray by differences that are more apparent than real. 



In the normal relationships of the tracks, the forefoot is placed in 

 front of the hind, but in the trackway now before me the forefoot is 

 occasionally found in the rear of the hindfoot. 



COLLETTOSAURUS PENTADACTYLUS Gilmore 



Plate I 



Collcttosaitnis pcntadactylus Gilmore, C. W., Smithsonian Misc. Coll., Vol. 80, 

 No. 3, 1927, p. 60, text fig. 2)2, pi. 19, fig. I. 



A trackway 1300 mm. in length, on slab No. 11,707, U. S. National 

 Museum (see pi. i) seems to be clearly referable to the above genus 

 and species. While this specimen adds nothing to our knowledge of 

 the feet impressions, the presence of a deep, continuous, but slightly 

 undulating, tail drag is of interest, since the type specimen (No. 1 1,527, 

 U. S. N. M.) showed none. A second specimen (No. 11,710, U.S. 

 N. M.) identified as pertaining to the same species, although 530 min. 

 in length, gives no evidence of a dragging tail. Study of these three 

 specimens confirms my previous conviction that the presence or 

 absence of a tail drag has but little significance as a diagnostic charac- 

 ter for distinguishing fossil tracks. 



ICHNITES FROM THE SUPAI FORMATION 

 Genus AMMOBATRACHUS, new genus 

 Generic eJiaraeters. — Ouadruj^edal. Five digits in pes, four in 

 manus. Forefoot smaller than hind, with the latter placed in front 

 of the former. Digits of both manus and pes widely separated, outer 

 toes of both much reduced in size, fifth of pes widely divergent. 

 Genotype. — Ammohatrachus furbatons. new species. 



AMMOBATRACHUS TURBATANS, new species 

 Plate J 



Type. — Catalogue number 11,691, U. S. N. M. Consists of a slab 

 of sandstone 380 mm. long having a trail traversing its entire length. 

 Collected by G. E. Sturdevant, 1927. 



Type locality. — Bright Angel Trail, Grand Canyon National Park, 

 Arizona. 



Geological occurrence. — Sui)ai formation, I'ennsylvanian. 



