I agree that the comb. of both names is interesting.
Parents of Robert Manwaring Dart are Robert Alexander Dart (b...1838,d.9/1924) and Josephine Faulkner (b..?1851 or July,1852, d.3/1925) although the more I look, the more dates,etc. I find. 1900 census has him listed as Robert M., not Robert A. I have found several Robert A.M Dart's( !?!) in the Groton, CT city directories....
Have you checked out the Bolton book on the Dart's? We were able to download it after emailing Frank Manning (from his posting) Another great resource is cheezz51 from this message board.
I'm stil very new at this but I am amazed at how much info. there is available!!