Single Table Inheritance

What am I doing wrong?

I have a simple MySQL table:

drop table if exists agencies;
create table agencies (
id int not null auto_increment,
type varchar(20) not null,
name varchar(255) character set utf8 not null,
primary key (id)
);

An equally simple Model:

class Agency < ActiveRecord::Base
end

class FotoAgency < Agency
end

Why can’t create an instance of FotoAgency in script/console? It seems
as the class hasn’t been loaded so far.

Best regards,
Oliver