The NGC 1961 group of galaxies.

Methods of determining the mass of the peculiar disc galaxy NGC 1961, alternative to those discussed by Shostak et al. (1982), are considered. If NGC 1961 is part of a stable group of galaxies seen in its proximity, its mass (within a radius of 244 kpc) must be approximately 10 to the 13th solar masses. If it is an interloper in this group, on the other hand, then at least 10 to the 12th solar masses of unseen matter is necessary to stabilize the reduce group. Furthermore, if the peculiar morphology of NGC 1961 is to be understood as the result of stripping by intergalactic material, this unseen matter must be distributed in an unusual fashion.