Grand Canyon of the Colorado. 339 



traces of rather slender claws, the apparent length of 

 which may be exaggerated by slipping (see fig. 1, b, ii and 

 iii). Palm of the manus apparently not impressing; 

 generally but three, sometimes four, subequal digits 

 imprinted in the track. Digits of both manus and pes 

 approximately parallel. 



Dimensions. 

 Manus. 



mm. 



"Width of impression 16-8 



Length of digit iii 5-8 



Pes. 



Width '. 21-0 



Length to tip of digit iii, without claw 18-2 



Length of digit i 4-8 



" ii, without claw 7-3 



" " " iii, " " 8-5 



" " " iv 12-2 



" v 6-0 



From tip to tip of outer digits 160 



Length of stride, same foot, 84-5, 60, 75, average 73-8 



Width of trackway 600 



The trail is nearly straight, the forward part of the 

 hand and foot rather deeply impressed, with a wave of 

 sand under the sole of the foot, so that approximately the 

 entire plantar aspect is recorded as shown in the figure 

 (fig. l,b). This might be interpreted as evidence of rapid 

 movement were it not for the foresetting of the beds. 

 As it is, the inference is clear that the animal was 

 advancing up the slope, which would not only account for 

 the greater relative weight borne by the pes, but also for 

 the banking of the sand beneath the sole. Were the fore- 

 set slope about 16°, the plantar impression would be 

 approximately level. As all the slabs in question were 

 detached from their original position, the actual dip 

 could not be ascertained (see article by Schuchert, fol- 

 lowing this). 



Laoporus noblei, n sp. 



(Plate II; text fig. 2.) 



Type specimen the second of the two Schuchert slabs, 

 catalogue number 2144, Yale Museum, supplemented by 



