What kind of car is it? A bass will fit in just about any car made if you maneuver it right. Most cabs I've seen are things like full size chevy caprices and ford crown vics, and a bass will fit in those with no problem.
Seeing how most taxis have a partition between the front and rear seats, you'll be sticking the scroll out the window and setting the body on your lap. Some cabbies drive minivans, if you're lucky one will come by when you need it. If you're at a hotel, let the bellman or consierge know you need the van style.