It appears that, historically (Gottlieb,
Thomson & Corwin 1998, personal communications), the label "NGC 3690"
refers to both of the two disk systems imaged here, and that IC 694
actually refers to the faint (mB=16.2 mag) compact object at the upper
right of this image (a.k.a. MCG+10-17-2a).
For now, I will follow the identification used by virtually all
investigators since 1959 in refering to the eastern portion of Arp 299
as IC 694 and the western portion as NGC 3690. (see
note 3 from NED for more details).
I would appreciate any amateur observations (by eye, not CCD or astrophotography) with a 16" class scope (comparable to the 16" refractor at the Rochester Observatory used by Swift, 1893, MNRAS, 53, 273, to discover IC 694) to verify that a galaxy as faint as MCG+10-17-2a can indeed be seen without prior knowledge of its existence. If not, it seems more likely that Swift instead subdivided NGC 3690 into two separate galaxies, with IC 694 referring to the eastern system. Please email me (jhibbard @ nrao.edu) if you make any such observations.