368 AXXALS XEW YORK ACADEMY OF SCIENCES 



fleshy portions of the limbs "^ere perhaps no more fish-like than in the 

 modern Xecturus. 



These Carboniferous footprints Yary widely in form, as do also the 

 known skeletons of Carboniferous Tetrapoda. The number of toes in 

 both manus and pes varies from three to five (G. F. Matthew. 1903. 

 1904), but in perhaps the majority of cases the manns has fonr digits 

 and the pes five, Abel (1912, p. 68) indeed concludes that no stego- 

 cephalian had a five-fingered hand; but in a well kno^n specimen of 

 Eryops megaceplialus (Amer. Mus., ISTo. 4186) which was described by 

 Cope (1880) digits I, III, TV, Y are present in the fossil and the missing 

 digit II is represented by a wide facet on carpal 2. 



One of the oldest known footprints is a single impression from the 

 Mauch Chunk Shale (Lower Carboniferous) of Pennsylvania to which 

 the name Thinopus antiquus was given by Marsh (1896). The imprint 

 consists of two stout, jointed toe-marks, which are nearly parallel to each 

 other, but separated by a considerable interval extending back to the mid- 

 dle of the palm ; from one of the toes a smaller offshoot near the tip indi- 

 cates a small lateral toe. It may be a mere accidental resemblance that 

 the pes of the modern Proteus is likewise bilobate, even in early stages 

 of development (Wiedersheim, 1892, p. 199). A footprint named Asperi- 

 pes avipes from the Carboniferous of Eastern Canada (G. F. Matthew. 

 1904, PI. II, fig. 2a, 2b) represents a three-toed manus that may have 

 been somewhat similar to that of Thinopus antiquus: but the pes of 

 Asperipes has five digits. 



Thus it is an open question whether the three- and four -toed feet of 

 Carboniferous Tetrapoda represent reduction stages from the t;\^ical 

 pendact}d cheiropterygium. or whether there has been an increase in the 

 number of the digits from three to five. Favoring the former supposition 

 is the following evidence : In modern Salamanders the number of digits 

 is four in the manus and five to four in the pes; in the pes the process 

 appears to have been reduction from five to four rather than the reverse : 

 for, (a) in the development of the pes of the four-toed Salamandrella 

 Jcayslerlingii there appears a vestigial fifth tarsal which later unites with 

 tarsal 4 (Schmalhausen, 1910, figs. 6, 7), and (h) in the degenerate 

 Proteus the number of digits is reduced to three in the manus and two 

 in the pes. 



In many of the Carboniferous footprints the fifth or outer digit of both 

 manus and pes is sharply divergent, the fourth is the longest and the ends 

 of digits lY, III. 11. I are turned inward, while the foot as a whole points 

 forward: all these characters suggest limb-structure fundamentally simi- 

 lar to that of Eryops or indeed of modern urodeles, especially the sala- 

 manders. 



