1893.) The Tilenstheriam Beda. 221 
different horizons as characterized by different and closely 
related forms is clearly indispensible in making an intelligent 
classification of any group of fossils, more especially when 
they are as highly specialized and as susceptible to the influ- 
ence of constantly changing environments as were the Titano- 
theriide. 
Yale Museum, Jan. 16, 1893. 
