"NGC 4660 in the Virgo cluster of galaxies". www.spacetelescope.org. Retrieved 2018-04-07. ↑ "New General Catalog Objects: NGC 4650 - 4699". cseligman.com. Retrieved 2018-04-05. ↑ Binggeli, B.; Sandage, A.; Tammann, G. A. (1985-09-01).