THE SQUIRREL PETAURUS. 
Petaurus sciuREUs. Geoff. 
In referring this beautiful little quadruped to the genus 
Petaurus, from the typical species of which it differs 
in the character of its teeth, we are influenced by no 
desire to set aside the established maxim that the teeth 
furnish the best means of distinguishing the primary 
groups of the Mammalia from each other. But there 
is no general law without an exception; and such 
exceptions occur too frequently in the department of 
zoology which at present engages our attention, to 
allow of the rigorous application of any artificial rule 
to the entire series, however generally correct may be 
the principle on which it is founded. 
Of the mischievous tendency of too pertinacious an 
adherence to a preconceived opinion of the value and 
