The getArea arguments are appended to the api call as such:
&getArea={name}
The possible arguments are:
Armorican
Belgic
British
Danube
East Anglia
Eastern
Gallo-Belgic
Gaulish (East Central)
Gaulish (South Western)
Gaulish (Southern)
Gaulish (West Central)
Germany
Greek
HAM
Iberian
LIN
MOU
North Eastern
North Western
Northern Italy
PAR
South Eastern
South Western
Southern
UNCERTAIN
Western
Several of these are to be deprecated as database clean up occurs. These will be removed from the documentation shortly.