This paper considers the linear theory of electromagnetic waves and instabilities in the solar wind in the presence of cometary ions with complete velocity shell distribution functions. A collisionless, homegeneous plasma, propagation parallel or antiparallel to a uniform magnetic field and frequencies below the proton cyclotron frequency are considered. If there is no relative drift speed between the cometary ions and the solar wind protons, both right- and left-hand polarized modes are stable, with ion cyclotron damping at wavenumbers of the order of the inverse cometary ion gyroradius. If there is a relative drift between the cometary ions and the solar wind protons greater than the Alfv¿n speed, both the ion/ion right-hand and left-hand resonant instabilities grow with maximum growth rates which increase as the shell distributions become narrower in velocity space. ¿ American Geophysical Union 1989