We do have an ops manual, but I don't recall anything reguarding duties of the crew members, except of course what the FAR's designate with requards to PIC duties. As Bolier said below your post we just have a trip sheet where we fill in names for the pilot flying for that particular leg, so as stated before, as a crew we understand that the person in the left seat for that particular leg is the PIC. If we do use contract pilots than myself for instance is the PIC for all the legs, even if I let the contractor fly from the left seat, because I am the only pilot in the airplane employed by the company, so at that time I am the only person responsible for the operation for the entire duration of the trip.