SCOTT: TOXODONTIA OF THE SANTA CRUZ BEDS. 
299 
cuboid. (15) There is an extensive articulation between the calcaneum 
and the fibula, except in a few typotheres which have suppressed this 
connection. 
While some of these resemblances are trivial and without taxonomic 
importance, it is difficult to believe that so many correspondences are due 
to a purely convergent mode of development and imply no community of 
origin. Indeed, there is but one very important structural difference 
between the Toxodontia (Notoungulata) and the Litopterna and that is 
the auditory region of the skull. Equally striking differences in the skull 
of the Rodentia are not held to justify the breaking up of that order. 
BIBLIOGRAPHY. 
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