OF THE MARSUPIALIA. 333 
called bicuspides; and that the three true molars on each side are not so displaced. So also in the lower 
Mammaiia, it is the canines, incisors, and false molars only which are subject to vertical displacement and suc- 
cession. ‘To the general rule, that in Marsupialia there are four true molars developed on each side of both 
jaws, there occur the two exceptions already noticed of Phalangista gliriformis and Petaurus pygmeus. Whether 
the genera Myrmecobius and Thylacotherium actually possess more than four true molars, as appears from ex- 
ternal form, can be determined only by ascertaining how many of the molar series are displaced and succeeded 
by others in the vertical direction. The Chrysochlore among the placental Fere offers a similar exception to 
the rule of three true molars in that group. 
