210 KANSAS UNIVERSITY QUARTERLY. 
given by Owen of a section of Mastodonsaurus. Indeed, had the 
tooth been found in Triassic deposits, without other evidence, it 
would be referred to that genus. Whether or not important struc 
tural differences in the labyrinthodonts are accompanied by differ 
ences in the microscopic tooth-structure I cannot say, but, until 
such is shown not to be the case, the present tooth may be referred 
to the genus MMastodonsaurus. 
from the difficulty of obtaining a sufficiently thin section of the 
very opaque material of which the tooth is composed, I have not 
been able to make a photograph showing the entire structure. 
Such, however, is unnecessary, as it will show but very little not 
already given by Owen for JZastodonsaurus. 1 give in an accom 
panying plate a half-tone reproduction of a photograph of a small 
portion of the tooth, showing under high magnification the minute 
structure of the dentinal tubules. 
The discovery of this tooth in the Kansas Carboniferous is of 
great interest, proving, as it does, the presence of true labyrintho. 
donts from a lower horizon than I can find any record of elsewhere. 
It is the only labyrinthodont hitherto discovered in America, I be 
lieve, aside from some fragmentary remains from the Triassic, 
described by Cope. The footprints of Amphibians, described by 
Marsh from the Osage beds, show very clearly that such animals 
were both diverse and abundant in the Upper Carboniferous times 
of Kansas, and it is not at all improbable that some of those which 
Marsh described were made by animals with teeth like the one 
described, inasmuch as the geological horizons cannot be far sep 
arated and may be identical. 
