You're welcome for the information.I am glad my Web site is helpful to you.
I think the Marcus Richardson you are looking for is #150 Marcus Calmes Richardson (1792-1864), son of Samuel Richardson and Catherine Bainbridge Hall.His headstone stated that he was in the 23rd Virginia Cavalry.He is on this page:
Here is the relationship between them: Major Fielding Helm Calmes' great-grandfather, William Waller Calmes, and Marcus Calmes Richardson's grandmother, Isabella Calmes, were brother and sister.
Put another way, Major Fielding Helm Calmes' great-great grandparents and Marcus Calmes Richardson's great-grandparents were the same--Marquis Calmes II (1705-1775) and Winnifred Waller (1708-1751).
By the way, the transcript of the slave interview I told you about related to #57 Dr. Francis Fielding Calmes (1794-1865), also a great-grandson of Marquis Calmes II, but not the Major Fielding Helm Calmes you are researching.I don't know how relevant it is to you.
Also, in your citation, you might want to list the home page of the Web site.