I don't like it as a fn because I feel like it's overwhelming. You'd definitely want to stick with a "normal" name as the other half of his given name.
Ptolemy RichardPtolemy AndrewPtolemy JamesPtolemy WilliamPtolemy GabrielPtolemy CameronMichael PtolemyDaniel PtolemyAaron PtolemySamuel PtolemyDavid Ptolemy