MARTIN: A GIGANTIC AMPHIBIAN. 105 



locate the form in a genus of reptile? or amphibians already known, 

 but for the present the footprints indicate an unknown animal. 



Additional characters are indicated in the apparent presence of 

 webs between the toes, extending; a short distance on the phalanges. 

 The body and the tail were carried clear of the ground, as there is 

 no evidence of dragging. This is all the more unusual in view of the 

 great depth of the impressions. The length of his sluggish stride 

 was 450 mm.; th.e manus was 90 nun. in length and the pes 104 mm. 

 Other detailed measurements are given in the description of the 

 plate. 



The most nearly related form is Baropus lentus, described by 

 Marsh, from the Coal IMeasures of Osage county, Kansas (1). The 

 present form differs from Baropus in being somewhat larger, and 

 especially in the indications of the heel pads and claws. None of 

 the other Coal Measures footprints from Kansas approach the 

 present footprints in size save Dromopus agilis Marsh (2), from 

 which it is clearly separated by a number of characters. 



The present series of footprints have been compared with the 

 descriptions of Coal Measures footprints given by King, Leidy, Lea, 

 Butts, Marsh, Mudge, Dawson, Moore, Cox, Moodie and Woods- 

 worth, a list of whose writings relating to this subject is to be found 

 in Moodie's memoir (2) on "The Coal Measures Amphibia of North 

 America." The present form is widely separated from the foot- 

 prints recently described by Lull (3) as Dromopus (?) woodworthi, 

 from the Coal Measures of Massachusetts. 



It has been assumed, on account of the indications of four toes on 

 the manus and five on the pes, that Onychopus gigas was an amphib- 

 ian, though the discovery of skeleton material may make this as- 

 sumption unwarranted. In view of the possibility of its being rep- 

 tilian, the present footprints have been carefully compared with 

 those described by Hitchcock (4), but none similar in form are 

 found. 



FORMATION. 



The massive reddish-brown sandstone in which the tracks were 

 found contains abundant flaky scales of mica. There are no per- 

 ceptible lines of stratification and no lines of cleavage. The rocks 

 are split up by horizontal, perpendicular and oblique cracks and 

 fissures into sections of erratic shapes and sizes (plate II). A care- 

 ful examination failed to reveal any invertebrates or other fossil 

 forms in the sandstone bluffs, although remains of Coal Measures 

 plants have been found elsewhere in this horizon. 



