This paper reports the results of simulations of the motion of dense suspensions of magnetotactic bacteria, bacteria that contain small magnetic dipoles. These simulations build on a previously described mechanism in which pair-wise, far-field, hydrodynamic interactions between swimming bacteria are proposed to be responsible for the band structure that appears when such bacteria are oriented in a given direction by an external magnetic field. Previous work has shown that these hydrodynamic forces act in a direction and with a magnitude that are fully consistent with the observed behavior. Applying this pair-wise, hydrodynamic force mechanism to hundreds of bacteria in a numerical simulation shows that band formation and stability is predicted by this simple model, while the precise band shape appears to depend on effects not included in the simulation.