[ANSTHRLD] Two Charges in Chief

[Eldwin Nightowl]

I'm sorry if someone's already answered this, but I will admit right now I'm pretty confused.
 
Is there a rule against having two charges in or on chief?  Specifically,

"Or, a mermaid in her vanity proper crined and tailed purpure, on a chief invected purpure a mullet voided and interlaced within and conjoined to an annulet Or."

Note that  Da'ud and Modar both provided backing for a mermaid proper (Caucasian skin color) with purple hair and tail if specified.
 
See http://eldwin.loveshade.org/images/ms_device11.jpg
 
Eldwin Nightowl