NO. 3 GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 35 



worms or annelids. The genus was characterized as " trackway a 

 single continuous groove." 



Genotype. — Unisukus inarshi Hitchcock. 



A specimen found in the Coconino sandstone bears a trail which 

 appears to have been made by some crawling, legless animal whose 

 affinities seem to fall in this genus. 



UNISULCUS SINUOSUS, new species 

 Plate II 



Type. — Catalogue number TI.498, U. S. N. M. Consists of a small 

 slab of sandstone carrying three trackways. 



T\fpe locality. — Hermit Trail, Hermit Basin, Grand Canyon Na- 

 tional Park, Arizona. 



Geological occurrence. — Coconino sandstone (about 150 feet above 

 base), Permian. 



Description. — Trackway a continuous groove having an average 

 width of 3 mm. and usually slightly sinuous. Sand on one side of 

 trail slightly raised forming a slight ridge ; the opposite side lower 

 and somewhat rounded. On the ridged side the wall of the groove 

 is nearly perpendicular, while the opposite side is beveled. At bottom 

 the trail gives the impression of being grooved rather than rounded. 

 The abrupt ending of one trail in the center of the slab as shown in 

 plate 1 1 suggests that it was made by an animal that was able to 

 move backward as well as forward. However, there is no accumula- 

 tion of sand at this end such as has been observed by Hitchcock in 

 trails of a somewhat similar nature. Slightly beyond the intersection 

 of two of these trails, both are flattened and widened out and the 

 bottom is sculptured by three distinct shallow, longitudinal grooves. 



( )f the JMesozoic ichnites assigned to this genus, the present species 

 most closely resembles Uni.uilcus inarshi in size and especially in 

 width of groove, but is at once distinguished from that form by the 

 more sinuous nature of the trackway, and by the grooved character 

 of the furrow. The reference of this specimen to the genus Unisukus 

 by no means implies that it is regarded as having been made by a 

 crawling worm, though such may have been the case. It seems more 

 probable that it is the track of a mollusk, for the dragging shell would 

 better account for the grooved appearance of the trail as well as the 

 ridge of sand on one side, although in living mollusks the trail is 

 usually ridged on both sides of the groove. 



The type is the only specimen of this species observed in all of 

 the hundreds of square feet of sandstone surface examined. 



