M94, sometimes nicknamed the "Croc's Eye Galaxy", is an unusal double-ringed spiral galaxy in the constellation of Canes Venatici. The inner ring with a diameter of about 5,400 light years, is a site of strong star formation, which is driven by gas forced into the ring by the galaxies inner oval-bar like structure. The much fainter outer ring has a diameter of about 45,000 light years and contains approx 23-25% of the galaxy mass & forms approx 10% of the new star formation. The outer ring has recently been shown to be a continuation of the galaxies spiral arms.
In 2008 a study showed that M94 may have very little, if any, dark matter.
For more info. see the Wikipedia entry.